Trail of Cthulhu Primer

How to Play Trail of Cthulhu

Keeper’s note: I’ve adapted much of what follows from this excellent rules summary. Except for the Dance Off For Sanity, I’ve altered the examples for our group.

The Keeper also notes that you may find this post, which runs through a session of Trail of Cthulhu and includes a description of the rolls and skills used, very helpful.

You may also want to look at the previous campaign I ran under Trail of Cthulhu, the Post Modern Masks of Nyarlathotep , which contains several useful examples of how the rules work.

How to Make a Character

The easiest way is to go to the Black Book Character Generator. Register as a new user. Please note that the answer to the question “Who is the author of The Call of Cthulhu? (One word, nine letters)” is case-sensitive in the most annoying way: Lovecraft with a capital-L. Do not make the same mistake as the Keeper and think that the site is broken for three months.

Please make sure to run any characters you generate with the site by me—I’ve already found a bug (Hobos need to buy down their Credit Rating, as a hobo can’t have a Credit Rating higher than 0) but overall it’s a really excellent site.

Get a clue!

Every ToC adventure consists of multiple Scenes, and in every Scene are clues that the players must find to further the story and help to solve the mystery. The players must utilize the abilities available to their investigators to root out these clues.

Ex. Ken’s character, Freddie, uses his Credit Rating ability on the wine and discovers that its from a kind of grape unknown to French viniculture!

Don’t have the correct ability for a scene? That’s not a problem because the players can still have their characters do a “simple search”. You don’t need a skill in Biology to dig around in someone’s drawers. All you need to do is to declare that you’re searching in someone’s drawers.

Ex. Rob says “While everyone is examining the body, my character is going to search the dresser in the bedroom.”

Whether or not you find anything, well…


Here are the basic occupations:


  • Army/Marines
  • Medic/Corpsman
  • Heavy Weapons/Engineer
  • Navy

Police Detective
Private Investigator

…I have a few other occupations culled from other sources if you’re interested. Please let me know what your concept is and we’ll work it out.

Each profession has a number of Occupational Skills; these are half cost.

Here are some suggestions for the best occupations to…

…know a lot: Antiquarian, Scientist, Professor, Author

…talk to people: Journalist, Private Investigator, Alienist, Clergy, Author

…steal stuff: Criminal, Hobo

…heal people: Doctor, Nurse, Military (Corpsman), Alienist

…hurt people: Military, Criminal, Police Detective, Private Investigator

…simulate a secret agent: Private Investigator, Police Detective, Dilettante

…simulate an athlete or other concept not covered: Dilettante


Where’s my Strength Score?

As befits a game about investigation, there are no “ability scores” in Trail of Cthulhu. You are free to interpret your abilities however you want, to reflect your concept; A high Athletics could mean both an acrobat and a weight lifter. If you wish, you may define as many “specialties” as you have Pillars of Sanity, and the Keeper will take this into account when resolving contests. Note however that if you lose a Pillar of Sanity, you will also lose a specialty.

A character in Trail of Cthulhu is defined by a series of skills and other characteristics, collectively called abilities. Before we go any further, you should understand the the three kinds of abilities:

Investigative Abilities

These are skills that allow your investigator to uncover information. You never need to make a die roll to use these skills; if you have the skill, and you ask to use it, and a clue is present, you find the clue.

You can use a point buy (see below) to find out more, or better information, or clues that are not easily discovered.

Investigative skills don’t use the same scale as General Abilities; a rating of 1 means that you are an expert, and a rating of 3 or 4 means that you’re a world respected authority (except for Credit Rating.)

I run Trail of Cthulhu in a slightly looser fashion then other people, closer in spirit to other games using the same system; generally speaking, Investigative abilities have the ability to not only uncover truth, but make things true. For example, in my previous campaign, I had players use Investigative spends to do things like…

…Convince a werewolf that you were a member of her pack (Biology)

…Throw a bundle of dynamite timed perfectly to explode right after you jumped out the window (Physics)

…Use a teleportation gate to bridge space and save your sister from cultists (Cthulhu Mythos)

I ask only that you be creative and try to respect plausibility.

General Abilities

These are closer to the traditional RPG definition of “skill”: Shooting, Driving, First Aid, etc. Unlike investigative skills, general abilities require a roll. Some general abilities (such as Mechanics) can be used as investigative skills under certain circumstances.

General abilities usually have more points; a rating of 4 or 5 indicates an above average competence, 8 or higher represents expert, and a rating of 12 is close to the edge of human competence.

Health, Sanity, and Stability

These are general abilities, but they are crucial to your investigator: Health is her “hit points”, Stability her “mental hit points”, and Sanity her “mental constitution”. See below for more details.

While there is no limit on how high an ability can go, the next highest ability must be at least half that of the highest.

For our campaign, Health and Stability are capped at 12 points, and Sanity at 10 points.

An easy way to remember the difference between Investigative and General abilities is Investigative abilities Uncover things—including making things true— while General abilities Do things.

Investigative Ability Example:

Keeper: Joe, you find Charleston splayed out on the floor. His chest has been ripped open.

Joe: I use Medicine to see if I know what did this to him.

Keeper: Something big, and with sharp teeth. Not a dog; maybe a big cat. You’d have to spend a point to know more.

General Ability Example:

Keeper: Russ, you find Colonel Pearkes splayed out on the floor. He’s bleeding from a gunshot.

Russ: I use First Aid to try and heal him.

Keeper: Roll…

Cthulhu Mythos

You can’t start with Cthulhu Mythos. (At least, not without my permission…) Cthulhu Mythos skill can only be acquired through encounters with the Mythos: creatures, gods, or tomes of Lore Man Was Not Meant To Know. Your maximum Sanity rating is 10 minus your Cthulhu Mythos rating.

Point spends with Cthulhu Mythos allow you to piece together bits of fragmented lore and obscure hints to get a sudden, chilling revelation about the mystery you are investigating, provided it has a Mythos connection. (Not everything does…) This gets you a blast of plot from the Keeper, but will almost certainly cause Stability and possibly Sanity loss, depending on the nature of the threat.

Special Investigative Skills

For this campaign, I’m adopting some rules from the Vampires vs. Spies game Night’s Black Agents: Contacts and Covers.

Both of these special skills act like General skills but must be purchased with Investigative build points. You get 3 points in either for one Investigative build point, i.e. spending 2 Investigative build points gets you a 6 point pool in either Contacts or Covers.


When you have a pool of Contacts, you can spend them to create a useful Contact at any time. You don’t need to create them beforehand; just spend the points, and describe them and what they do.

Example: Jimmy Wright has 9 points of Contacts remaining and needs a lawyer in Paris to help get his friends out of a jam. He spends 4 points to create Hector DuBois, a respected Parisian barrister who owes him a favor.

Once points are allocated to a Contact, they can’t be recovered; you have to use experience points to refill the pool.

You can spend points allocated to a Contact in order to get information or do things for you. Once all the points allocated to a Contact are spent, that Contact can’t help you anymore (they’re burned.)


Covers work similarly to Contacts—you spend points out of your pool to create a Cover identity. Covers are much more valuable than mere disguises; Covers have actual legal existence and can get you places a simple disguise won’t.

Example: Still in Paris, Jimmy discovers he needs to find out what Alphonse, the head of the local Cult of Nyarlathotep, is up to. As befits a Cultist, Alphonse is extremely paranoid and won’t let even someone wearing Cult robes come up to him. Jimmy spends 3 points from his Covers pool to create a Cover identity: John Matchington, a British dabbler in the occult. Using this identity, he is able to get a meeting with the reclusive Alphonse.

Like Contacts, points allocated to a Cover can’t be refreshed or recovered; you have to use experience to build back up your pool. When you’ve spent all the points allocated to your Cover, it’s burned and can’t be used anymore.

Refreshing Pools

Points spent are not lost forever, provided the ability rating remains the same. However, they refresh at different rates.

  • Investigative abilities refresh when you are finished with the current investigation. For this campaign, this will occur when I think you have finished one of the main chapters in the story, of if enough sessions have passed since the last refresh.
  • Once (possibly twice) per session, if your investigator reaches a place of safety, you may choose up to three General Abilities to refresh, except for Health, Sanity, or Stability.
  • Athletics, Driving, Firearms, Fleeing, Firearms, Piloting, Riding, Scuffling, and Weapons fully refresh whenever 24 hours of game-world time elapses.
  • The Health pool refreshes over time, at a rate of 2 points per day of restful activity.
  • Wounded characters need First Aid and then recovery time to heal; we’ll go over this when it happens.
  • During a session, a character can refresh some Stability by having scenes with her Solace or her Symbol.
  • To refresh Stability between investigations, the Investigator must spend calm, undisturbed quality time with his Solace, allowing him to forget the shadowy world of the Mythos for a moment.

Skills Ratings and Points Pools

To be trained in a skill, a player must have at least a rating of 1. The rating value also determines the amount of points the player has in that particular skill. A character with a rating of 4 in Intimidation has 4 points in their Intimidation pool. If they spend a point, their pool goes down but the rating does not.

Points and Benefits

Sometimes the Keeper will ask the player if they’d like to spend a point from a skill to gain a benefit. These benefits can vary from extra info or extra firepower or a new contact.

GM: If you’d like, you can spend a point in Intimidation to get a little bit of extra info from the snitch.

Russ: Sure, I’ll spend that point and press the muzzle of my gun against his kneecap.

GM: You’re able to convince Wally the Weasel to give you the name of his employer and purchase some extra firepower, if you so choose.

So the investigator still has a rating of 4 in Intimidation, but only 3 points left in his Intimidation pool.

Point spends can be very powerful and are ways for you to affect the plot (see above).


There are just some times when the only way to solve a problem is with a good die roll and the only die you’ll need is a D6. Yup, the plain ones. The only abilities that need dice rolls are the ones listed under General. The Keeper will tell the player that he needs to roll a skill check, and he then needs to roll higher or equal to the Difficulty Number, which the Keeper may or may not tell you.

Difficulty Numbers (DN) range from 2 to 8. Whoa, whoa, WHOA. Hold on now. How do you get an 8 on a six-sided die? By Point Spends. For every point you spend, that’s +1 to your die roll. The players just need to remember that they have to declare how many points they’re spending BEFORE they roll the die.


Keeper: As Charleston drives up the narrow mountain road, the skies darken and unleash torrents of rain down up him. The road becomes slick with mud and visibility is reduced to almost nil. I’d like a skill check for Driving and let’s say the DN is 4.

Russ: Let’s see…Charleston has a Driving rating of 6, so I have 6 points to spend. I’m going to spend 2 points for this roll. I rolled a 3, so my total is 5. I passed!

Keeper: Despite the treacherous weather, you’re able to keep your car on the road and drive safely to the top of the mountain.

It’s a very easy system. The only hard part is having players remember that they have to declare the point spend BEFORE THEY ROLL.

Dance Off for Sanity

There are times when a PC goes up against a PC/NPC and the only way to solve things is a dance off, or as it’s called in the book, a contest. Each character does a skill check, spending points and rolling dice, and the first one to fail their check loses the contest.


DANCE OFF w/ Colonel Pearkes (Athletics 10) vs Cultist (Athletics 8)

Keeper: Colonel Pearkes, you’ve run onto the dance floor, hoping to get lost in the crowd. Unfortunately, a kicking song just started playing, and the dance crowd has formed a circle around you as the cultist bursts through. OH DANG, THE CROWD WANTS A DANCE BATTLE! What’s your first move, Joe?

Joe: I’m going to spend 1 Athletics point and do the Worm.

Keeper: Ok, the Worm’s DN is 3. Go for it.

Joe: Rolled a 2! Success!

Keeper: You worm your way across the dance floor, but the crowd and the cultist aren’t impressed. “So this is Toronto dancing?” the cultist says. He’s going to spend 2 Athletics to do a windmill, DN 5. The cultist rolled a 4 for a total of 6! The crowd is going wild over the speed of the windmill!

Joe: I need to step up my game before I get served. The Superman.

Keeper: Ok, DN 6. Roll for it.

Joe: DN 6?! Ok, I’m gonna spend 3 points first. And I rolled a …3. Thank god I spent those 3 points!

Keeper: Ok, ok, you did the Superman fairly well, but not enough to sway the crowd. The cultist, thinking he has it in the bag, is going to spend 1 point and do an Armchair Freeze, DN 3. He got a 1! He failed his roll and fell straight onto his face!

Joe: I’m booking it.

Keeper’s Note: Cthulhu needs more dance-offs.

Fist vs Tentacle

There comes a time when book smarts aren’t enough and you just got to plant a fist into something’s squishy face. And that brings us to combat.

The Basics

The Hit Threshold is the number to beat to connect with your target. For Investigators, their HT is 3, but if their Athletics skill is 8 or higher, the HT increases to 4.
Just because a character doesn’t have a particular skill doesn’t mean they can’t use it. No rating in Firearms? No problem. You can still shoot a gun. You just won’t do as much damage. In fact, you do -2 to all damage rolls and that’s on top of the bonus/penalty for whatever you’re using. This rule applies to Firearms, Scuffling, and Weapons.

Firearms goes to firearms.

Scuffling goes to fists, feet, and things like knuckle dusters.

Weapons are for things like swords, knives, maces, etc.


Whoever picks the fight, start the fight. Doesn’t matter if you’re shooting, stabbing, punching; the person that starts the fight gets to go first.

Ex. 1

Keeper: Tony “The Rat” Wilkins is standing directly in your path. There’s no way he’s going to let you through the door.

Russ: I punch him in the face.

Keeper: Roll to see if you hit.

Ex. 2

Keeper: Tony “The Rat” Wilkins is standing directly in your path. There’s no way he’s going to let you through the door.

Joe: I shoot him in the face.

Keeper: …roll to see if you hit.

Ex. 3

Keeper: Tony “The Rat” Wilkins is standing directly in your path. There’s no way he’s going to let you through the door.

Ken: I stab him in the face.

Keeper: …roll to see if you hit.

Getting Hurt Sucks (Don’t Do It)

As long as your Health is in the positives, there are no special rules. It’s when you drop into the negatives that you have to start worrying. And once you hit -12, you’re dead. And the nearest cleric is four genres and two game systems over.

Starting at -1, the player has to start making Consciousness rolls to stay awake. The DN to stay conscious will always be the absolute value of your current health. So if you’re at -1, you have to beat DN 1. -4, DN is 4. Of course, you can spend points from your Health pool to stay conscious but the DN will be the number before you chose to spend points.


Keeper: Freddie’s just been shot! His health has dropped to -3. Make a consciousness roll.

Ken: Ok, I don’t want to chance it, so I’m going to spend 2 Health points. I rolled a 2 for a total of 4, so I stay conscious but my Health is now at -5.

You can NEVER spend Health points if it will drop you Health to below -11.

Other Health rules

Health is between 0 to -5:
You make a Stability check to use Investigative spends and the DN for all tests increases by 1.

Health is between -6 to -11:
You lose 1 Health point every half hour until you receive aid. And even if you succeed on your Consciousness roll, you can’t fight or take any actions.

Health is -12 and below: DEAD

Pull Yourself Together!

Stability is your mind’s immune system. The higher the rating, the stronger it is and the less likely you are to snapping. Sanity is how much of your mind is left after having been exposed to the Cthulhu Mythos. Since Stability is the one dealt with more often, let’s start with it.


There are just some times when you witness something that just messes with your brain. And that’s when you start to lose Stability.

For this campaign, I’m going to use a modified Stability system that charges fixed costs rather than asking for rolls. Stability loss ranges from 0 (seeing a corpse) to about 5 (killing your own Solace.)

You may notice that I included something that costs 0 Stability above. That’s because if the thing that is causing Stability loss is associated with the “Cthulhu Mythos” (aliens, magic, Outer Gods), the cost is one point higher. Finding a random human corpse is a 0 point Stability loss; finding the corpse of a Deep One is a 1 point stability loss.

Like Health, things happen if your Stability drops below 0.

Stability at 0 to -5 is SHAKEN: All DN’s for checks increase by one and you can’t spend investigative points.

Stability at -6 to -11 is BLASTED: You gain a mental illness! And it’s permanent! You also lose 1 points from your Stability rating. You can always buy it back.

Stability at -12 and under is INSANE: You are officially cuckoo for cuckoo puffs. You got one chance to go out in a blaze of glory or you can consign yourself to a mental ward.

There are several ways to regain Stability. Stability points refresh after a adventure/session or the player can have the investigator follow their Drive.

Sources of Stability

For this campaign, you have two Sources of Stability. Everyone has both of these when we start play.

Your SYMBOL is a physical object that has some meaning to you, ideally connected with your Drive. Examples might be dog tags, a letter from your father, your trusty kukri, or the picture of your lover. Once per session if you have a few minutes to spend with your Symbol and thinking about what it represents to you, you may refresh 1 point of Stability.

Your SOLACE is the person who keeps you going—a lover, a family member, your mentor, or maybe just your favorite bartender. If you can spend six hours of uninterrupted time with your Solace—an evening of intimacy, a long family dinner, some time working in the lab together, or going on a bender and reminiscing about old times—you can refresh 2 points of Stability.

In between sessions, if you can spend a day with your Solace (or the equivalent) you can refresh ALL Stability.

Note that for both Symbol and Solace refreshes, you need to not be in a situation of imminent danger.

If a session is scheduled to last longer than about 4 hours, I’ll generally allow a second refresh from both Solace and Symbol.


There’s only two ways to lose Sanity. And the best way to say it is straight from the book!

  • A Mythos shock drops your Stability pool to 0 or below.
  • You use the Cthulhu Mythos.

If you lose Sanity, you lose Sanity. You can’t roll to avoid Sanity loss.

What’s a Mythos Shock? It’s when the investigator witnesses a Mythos-related event and it drops the Stability score.

If the character is SHAKEN by the mythos, the Sanity raiting drops by 1 point.

If the character is BLASTED, the Sanity raiting drops by 2.

If both happen, you’ll only suffer one of those losses during any given adventure. Yes, the more severe loss.

Now there are some ways to keep your Sanity and they’re pretty awesome for roleplaying.

Denial – If no evidence exists at the end of the adventure, then it must have been all in your mind. At the Keeper’s discretion, the player may be required to take on a mental illness or make up a story about what you think happened to what really happened. If the player ever uses info that he shouldn’t remember, the Keeper can take a Sanity point from the player.

Fainting – Yup! If something so terrifying occurs and the investigator stands to lose more than 1 Sanity point, the player can declare that the investigator faints dead away and will only lose 1 Sanity point. They keep their Sanity but they’re not allowed to participate for the rest of that particular scene.

But keep in mind that if the investigator faints and the team ends up running away, someone may be left behind…

Pillars of Sanity

For every three points of Sanity RATING you have, you must define a Pillar of Sanity. These are the core beliefs your investigator holds to; they can be damaged by encountering the Mythos. Here are a few examples:

• Family (especially family honor, purity of one’s blood, and suchlike)
• Human dignity and value
• Scientific progress or the value of the intellect
• Physical laws and the reality of scientific knowledge
• The goodness, beauty, or worthiness of Nature or the environment
• The innate goodness of mankind
• Moral principles
• Aesthetics or the high principles of art
• Epicureanism; living life to the fullest
• Patriotism and national virtue
• Love of one’s home city or town


Your Drive is the reason you do things. It’s the “why” you decide to venture down an dark alleyway (Curiostiy) or the “why” you won’t stop hunting the man in black (Revenge).

When you follow your Drive, you can regain Stability points. If you don’t follow it, you can lose stability points.

Hard Driver

If the Keeper thinks your Drive would really, really motivate you to do something, that’s called a Hard Driver. Resisting a Hard Driver costs 4 Stability points. If you give in to the Hard Driver, you gain 2 Stability points.

Soft Driver

If the Keeper thinks you should probably do something because of your Drive, that’s a Soft Driver. Resisting a Soft Driver costs 2 Stability points, and giving in to it gains you 1 Stability point.

Drivers should (and won’t!) not replace roleplaying; however, this is a horror game, and that will require your characters not act like D&D murderhobos. (I kid.)

You are perfectly justified in pointing out to the Keeper that you are following your Drive and should earn Stability. The Keeper cautions you that Drivers only occur when the situation would be made worse by following it.

Trail of Cthulhu Primer

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