Call of Cthulhu 7e Scenario Design Guide

Introduction

A Call of Cthulhu scenario is not a trail of rooms that investigators must visit in the correct order. It is a dangerous situation already in motion. Something happened before play began, someone wants something badly enough to conceal or pursue it, and the investigators have enough evidence and motivation to interfere.

Good design gives the Keeper a stable truth and gives players several ways to discover and change it. The antagonist's plan can continue. The clues can travel through different locations. The ending can be uncertain. What should not be uncertain is whether the players have meaningful choices to make.

This guide provides a repeatable way to build original Call of Cthulhu 7e scenarios. It is deliberately useful for one-shots and campaign episodes alike. For running the material during play, use How to Run Call of Cthulhu 7e. For the broader Keeper workflow, start with the Keeper Resources Guide.

Hot Take

The climax is the least useful place to start designing a Call of Cthulhu scenario.

An image of investigators confronting an impossible thing in a lighthouse, mine, or ruined church can be inspiring. It is not a scenario until you know why the investigators go there, what they can learn before they arrive, what happens if they choose another route, and what they might decide to do once they understand the danger.

Start with the trouble already underway. The climax will emerge from the choices that trouble forces.

Start With a Situation, Not a Plot

A plot tells you what happens in order. A situation tells you what is true, who is acting, and what will happen if no one intervenes. The first can be useful for a novel. The second is more useful for an investigation game because players decide the order of events once play begins.

Write your scenario in this compact form:

Because [past event], [antagonist] now wants [objective]. They are doing [current actions]. If nobody intervenes, [escalation or outcome]. The investigators become involved because [immediate hook].

Example:

Because a shipping family concealed an artifact in a coastal warehouse decades ago, the heir of a failed antiquarian now wants to recover it before the building is demolished. They are bribing dockworkers, falsifying cargo records, and silencing a former partner. If nobody intervenes, they will open the artifact during the next spring tide and release something into the harbor. The investigators become involved when the former partner arrives at a hospital carrying a water-damaged ledger and dies before explaining why they sought them out.

This paragraph gives you a history, a current plan, a timeline, an opening, people to portray, places to visit, and evidence to distribute. It does not tell the players that they must search the hospital, then visit the warehouse, then fight the heir. That freedom is the point.

Choose a Strong Scenario Question

The scenario question is the investigation's central uncertainty. It is not necessarily the same as the hidden truth. The group starts with a question they can understand, then discovers that the answer is larger, stranger, or more costly than it seemed.

Good starting questions are concrete:

• Why did a reliable person vanish after receiving a particular letter?
• Who is staging the accidents around a construction site, and why?
• What is making a family ill after they move into an inherited house?
• Why are several unrelated witnesses describing the same impossible sound?
• What did a dead collector remove from the museum before their death?

Avoid starting questions that require the investigators to already accept the Mythos. "Which Outer God is behind this?" is a late-stage question. "Why did the astronomer destroy their own telescope?" gives the group a person, an event, physical evidence, and a reason to investigate even if no one believes in anything supernatural.

The question should point to action. A mystery without an affected person, a location, a deadline, a consequence, or a possible source of evidence is difficult to start. Give the group a first place to go and at least one person to talk to.

Write the Hidden Truth

The hidden truth is the Keeper's answer key. It must be clear enough that you can improvise from it without contradicting yourself. Keep it short, factual, and independent of what investigators do.

Answer these six questions:

Do not write, "The investigators discover that..." in this section. They might not. Write what the cult leader has already done, which record was forged, where the victim is being held, and what happens at midnight. The hidden truth ends at the moment the game begins. After that, the story belongs to the table.

Keep a distinction between the antagonist's belief and reality. A cultist may misunderstand the ritual they are attempting. A collector may think an artifact grants wealth when it instead attracts predation. A terrified witness may sincerely report the wrong cause. This creates room for investigation without making every NPC a liar.

Build Layers of Mystery

Call of Cthulhu scenarios work well when each answer creates a deeper question. The Keeper Rulebook describes this as peeling an onion, and suggests that each layer give the investigators two or three choices about where to go next. The group should rarely receive a final explanation from its first clue. Instead, evidence changes the problem from a familiar concern into something more dangerous.

Think in layers:

The layers do not have to be a single straight chain. A group may learn the hidden mechanism before identifying the human cause, or meet the antagonist before finding the first record. The value of layers is that every discovery gives the players a new question instead of ending the session with a fact dump.

Do not make every layer "more lore." A layer can be emotional or practical. Learning that a witness is protecting their child changes the interview. Discovering that the missing person left willingly changes the rescue. Finding that the building will collapse at dawn turns research into a time problem. Mystery is not only hidden names and ancient history.

Design a Redundant Clue Web

The core design rule is simple: every conclusion the investigators need should have multiple evidence paths. One clue is a bottleneck. Several clues make an investigation resilient to failure, unexpected priorities, and player creativity.

For each necessary conclusion, create at least three clues that differ in source or method:

These are not three versions of the same clue. They approach the same conclusion from different directions and allow different investigators to contribute. A social group can learn from a witness. A research group can find records. A cautious group can observe a consequence. Each route confirms the truth in its own way.

Assign clues to places, people, and events, not to a mandatory sequence. If the group does not visit the dock office, the forged record might be found in a shipping archive, through a union contact, or in the heir's discarded correspondence. Preserve the clue's meaning while changing its delivery logically.

Core, supporting, and advantage clues

Classify each clue before play:

• Core clues keep the case moving and should be reachable through ordinary investigation. Do not bury them behind a single failed roll.
• Supporting clues confirm a theory, explain context, or reduce ambiguity. They reward careful research and social play.
• Advantage clues make the final plan safer, faster, or more effective. They reward cleverness without being required for survival.

This structure lets you honor success without making progress depend on perfect dice. It also gives you a quick answer when players ask what a strong success changes: it grants an advantage clue, improves the timing, or reveals a complication before it becomes dangerous.

Give the Antagonist an Active Timeline

The antagonist should act while investigators investigate. A static villain makes delay free and turns every clue into an academic exercise. An active timeline makes the scenario feel alive without requiring the Keeper to force scenes.

Write three to five escalating events that occur if the investigators do nothing or fail to prevent them. These should be visible through consequences, witnesses, news, environmental change, or direct contact.

Do not advance the clock simply because the group paused to think. Advance it when time passes in the fiction, when an action makes the investigators visible, when a roll failure has that consequence, or when the group knowingly chooses another priority. Tell the group enough that they can judge the cost of delay.

The antagonist should respond to investigator progress. If they learn the group is asking questions, they may lie, bargain, threaten, move evidence, set surveillance, frame the investigators, or accelerate their plan. These responses create new scenes because they follow from the world, not because the Keeper needs an encounter.

Create Locations That Change Play

A location should offer more than a description and a search roll. It should change what the group can know, do, risk, or obtain.

For each location, prepare five entries:

1. Immediate impression: What does an investigator notice on arrival?
2. Question: What can the group learn or accomplish here?
3. Evidence: Which clues, objects, or people are available?
4. Pressure: What makes remaining, searching, or returning costly?
5. Connection: Where can the evidence point next?

Example: an abandoned greenhouse may look recently tended despite broken glass. The group can learn who is harvesting a rare plant. Evidence includes delivery labels, muddy tracks, a hidden notebook, and an exhausted caretaker. Pressure comes from poisonous fumes, an approaching owner, and the fact that the plants react after sunset. The connection is a supplier's address and a name in the notebook.

Do not make every location a hostile maze. An archive can be a safe research scene with social risk. A cafe can provide a contact and a place to be watched. A hospital can establish medical facts and introduce a worried relative. Variety lets investigators use different skills and makes the dangerous locations more memorable.

Design NPCs as Pressure Points

An NPC exists to change the group's options. Give important people a goal, a fear, a resource, and a threshold. The threshold is what it takes for them to cooperate, panic, betray someone, or act against their normal interest.

The most useful NPCs are not all allies or all obstacles. A person can provide a clue while creating a cost. The foreman gives access but expects silence. The retired sailor helps only if the group keeps a promise. The heir offers a deal that reveals a real danger but serves a selfish aim.

Give NPCs plausible knowledge. A hotel clerk knows guests, deliveries, and rumors, not the entire occult history of the town. A cultist may know their assigned task but not the leader's ultimate plan. This creates a trail of partial truths instead of a single exposition speech that empties the scenario.

Make the Opening Impossible to Ignore

The opening scene does not need a gunshot, corpse, or monster attack. It needs a problem with enough personal, practical, or moral pressure that the investigators have a reason to respond.

Strong openings usually combine two elements:

• Connection: The victim, request, place, or evidence matters to at least one investigator.
• Motion: Something has already changed and will become worse if ignored.

An anonymous letter with no context is weak because it can be ignored. An anonymous letter that quotes a private detail, arrives with a damaged personal object, and warns that a named person will disappear at sunset is a playable opening. It gives the group a person, a mystery, a deadline, and a first line of inquiry.

Use player backstories with permission. Ask whether a friend, mentor, former employer, rival, relative, or old case is available as a hook. Then connect that hook to the existing situation rather than making the character's entire history secretly about the Mythos. The investigator should feel involved, not rewritten.

Use Handouts as Investigative Tools

A handout should do work the spoken description cannot. It lets players compare dates, recognize a repeated name, notice an omission, handle a map, or argue about what the evidence means. It should never require copying a page of source material into the scenario.

Useful handouts include:

• A damaged letter with a missing line and a return address.
• A map marked with three locations and a route that stops abruptly.
• A photograph that contains an object later found in a different place.
• A receipt, ledger page, or train ticket that contradicts an alibi.
• A short newspaper clipping that establishes a past event and an unexplained detail.

Keep text short and legible. Use dates, names, relationships, and inconsistencies rather than dense prose. If the group must know a fact to proceed, make that fact readable without a decoding puzzle unless the puzzle itself is the intended scene.

For a digital table, share a clear image or readable text. Do not hide a required clue in a low-resolution scan or expect players to infer important details from decorative fonts. The mystery should arise from interpretation, not from accessibility failure.

Choose a Scenario Structure

There is no single correct structure. Choose the smallest structure that supports the group's experience and your preparation time.

Linear investigation

A linear scenario has a clear beginning, middle, and end, with a limited sequence of likely developments. It is a good first design for a new Keeper, a convention game, or a session with a fixed time limit. The group may take small detours, but the central evidence points toward a known climax.

Linear does not mean railroading. Provide choices within each stage, let investigators solve obstacles by different methods, and allow the consequence of failure to change the final confrontation. The goal is a clear arc, not one approved door.

Node-based investigation

A node-based scenario offers several locations, people, or leads from the opening. Each node contains information that points to other nodes and eventually to the central threat. This is the most reliable shape for an investigative one-shot because it supports player choice without demanding a full sandbox.

Prepare four to six nodes, give each two or more connections, and make sure no required conclusion depends on one node alone. The warehouse, archive, relative, and shipping office can be visited in any order. The antagonist timeline makes the order matter without making an incorrect order fatal.

Sandbox or campaign situation

A sandbox establishes a place, factions, resources, tensions, and timelines, then lets the investigators choose what to pursue. It works best for an ongoing campaign where the group wants to revisit locations and shape long-term consequences.

Do not script the ending. Prepare what the factions will do if unchecked and update that timeline after each session. The campaign's story grows out of the collision between investigator choices and active forces in the setting.

Plan Action and Horror for a Purpose

Action and horror should reveal something, change access, raise the cost of delay, or force a meaningful choice. They are not interruptions added because the investigation has been quiet for twenty minutes.

Before an action scene, answer these questions:

• What does each side want?
• What objective ends the scene?
• What terrain, exits, and obstacles affect the options?
• What clue, consequence, or relationship changes afterward?

A chase can show where a cultist goes, force the group to choose between pursuit and an injured ally, or leave the investigators with the villain's dropped evidence. A fight can buy time to protect a witness or reveal that ordinary weapons will not solve the problem. If the scene would not change the investigation, summarize it or remove it.

Horror works the same way. Decide what the disturbing event teaches: the threat has reached a new place, a trusted explanation is false, someone has changed, or the investigators now understand the cost of waiting. Show the normal world first, then introduce one impossible detail that the group can observe and test. Save the largest revelation for the moment it changes what the group can do.

The Combat and Chases Guide and Sanity System Guide explain the relevant player-facing procedures. Use them to make danger legible, not to trap the group in an unwinnable scene without information.

Prepare Endings, Not an Ending

Write several possible outcomes based on what investigators might accomplish. Do not decide which one they must reach. A scenario can end with containment, rescue, exposure, destruction, negotiation, escape, compromise, or survival with a problem deferred.

For each outcome, note:

• What must the investigators understand or obtain?
• What action could produce this outcome?
• What does it cost?
• What changes in the world afterward?

Do not require the group to kill the antagonist. In Call of Cthulhu, stopping a plan, saving people, learning the truth, escaping with proof, or surviving to act again can all be victories. Conversely, a dead villain is not always a solution if the ritual, artifact, evidence, or larger organization remains.

After the climax, make consequences visible. Who survives? What does the public believe? What did the investigators lose? What clue or debt remains? A short aftermath turns a sequence of scenes into a complete story.

Build a Scenario From Scratch

Use this sequence when you need a playable original scenario quickly.

1. Choose an ordinary starting world. Pick a town, institution, family, workplace, expedition, event, or social circle the players can understand.
2. Introduce one wrong thing. A missing person, altered object, unexplained death, pattern of accidents, impossible observation, or secret purchase is enough.
3. Write the hidden truth. Define the past event, antagonist goal, current action, horror signature, and outcome if unopposed.
4. Write the opening. Tie the wrong thing to the investigators and give them one immediate lead.
5. Name four nodes. Create people, locations, or sources the group can pursue in any order.
6. Create three clues for each necessary conclusion. Spread them across social, documentary, physical, and observational routes.
7. Write the antagonist timeline. Add three escalating moves and decide what makes each visible.
8. Prepare two useful NPCs and one dangerous NPC. Give each a goal, fear, resource, and threshold.
9. Choose one action scene and one horror revelation. Give each an investigative purpose and an alternate route around it.
10. List possible endings. Include at least one success that does not depend on killing anything.

This can fit on two pages of notes. Add detail only where it supports the particular people, places, or evidence the group will encounter. A scenario becomes more playable by having clear connections, not by having a long history section no investigator can discover.

Scenario Design Checklist

Before play, confirm that the scenario has:

• A one-paragraph situation explaining the past event, current threat, and opening hook.
• A central question the investigators can understand without Mythos knowledge.
• A short hidden truth that ends when play begins.
• Several layers of discovery, each creating a practical new question.
• At least three evidence paths to every necessary conclusion.
• Core clues that remain available after ordinary failure.
• An antagonist timeline with visible, logical escalation.
• Locations that each offer evidence, pressure, and a connection onward.
• NPCs with goals, fears, resources, and limits.
• Handouts that create questions rather than decorative reading.
• An opening that supplies both connection and motion.
• Action and horror scenes that change the investigation.
• Several possible endings and consequences, not a scripted conclusion.

The best scenario notes tell you what happens once the investigators act, and leave what they will do to them. Give the world a past, a present danger, and enough evidence to be understood. Then let the group decide whether the truth is worth facing.