Achtung! Cthulhu 2d20: Running Your First Mission in the Secret War

Quick answer

Run your first Achtung! Cthulhu 2d20 mission as a short, self-contained operation: brief the squad, give them one clear objective and one hidden horror, and let Momentum and Threat do the pacing work. Prep three scenes, not a plot, and stop before the mission overstays. If you want a ready-made structure, the Achtung! Cthulhu 2d20 starter set gives you pre-generated agents and a first mission to run straight out of the box.

Your first Achtung! Cthulhu 2d20 mission does not need a campaign bible. It needs a clear objective, a handful of scenes, and a table that understands how Momentum and Threat push the story forward. The Secret War setting rewards tight, pulpy operations: infiltrate, investigate, confront something that should not exist, and get out before the Nazis or the Mythos finish the job.

This guide walks through the order I use when running a new group: read the mission, build or hand out agents, frame the opening scene, escalate with the 2d20 system, and close the operation with consequences that matter. Each step includes the mistake that most often derails a first session, so you can avoid it before it happens.

Step 1: Pick a mission you can run in one sitting

Start with a single operation, not a campaign. A good first mission for Achtung! Cthulhu 2d20 has one location, one primary objective, and one Mythos complication. If you are using the starter set, run the included mission as written before you homebrew anything. If you are building your own, write the objective in one sentence: recover the artifact, extract the defector, or sabotage the ritual site.

Keep the scope small enough that you can finish in three to four hours. First sessions die when the GM over-prepares a sprawling plot and the players spend the night in one room. A tight mission also teaches the 2d20 rhythm faster, because every scene has a clear reason to spend Momentum or add Threat.

• Checkpoint: can you describe the mission in two sentences? If not, cut a scene.
• Common mistake: prepping a campaign arc instead of one operation.

Step 2: Build agents with the mission in mind

Achtung! Cthulhu character creation is fast when you tie each agent to a job in the squad. You want someone who can talk, someone who can fight, someone who can sneak or investigate, and ideally someone with a reason to know about the supernatural. Ask each player what their character did before the war, then pick the skills and talents that support that answer rather than chasing an optimized build.

If your group is new to 2d20, use the pre-generated agents from the starter set for the first mission and let everyone rebuild afterward. That removes decision paralysis, gets you playing in twenty minutes, and shows how the system's attributes, skills, and focuses interact before anyone commits to a long-term character.

• Checkpoint: every agent should have one thing they are clearly best at.
• Common mistake: letting one player build a generalist who steps on everyone else's scenes.

Step 3: Frame the opening scene with a clear objective

Open in motion. Give the squad their orders, their cover identities, and the first concrete problem before anyone rolls dice. A briefing scene is fine, but keep it under ten minutes and end it with a decision: how do they get in, who do they talk to first, what do they leave behind? That decision is what makes the rest of the mission feel like the players' operation rather than your script.

State the stakes out loud. In the Secret War, failure usually means the enemy completes a ritual, a town gets sacrificed, or the Mythos gains a foothold. Players engage harder when they know what happens if they walk away.

• Checkpoint: the players should be able to restate the objective in their own words.
• Common mistake: opening with a long lore dump instead of a decision.

Step 4: Use Momentum and Threat to control pace

The 2d20 system tutorial part that matters most at the table is the economy between Momentum and Threat. When players roll well, they bank Momentum and spend it on extra dice, extra information, or a better position. When they push their luck or take complications, you bank Threat and spend it later to make their lives harder. That back-and-forth is the engine of the session, not a side rule.

Spend Threat visibly. If you hoard it, players stop feeling the cost of their choices. If you dump it all at once, the mission feels punitive. Aim to spend a point or two at a dramatic moment: a patrol arrives, a door locks, a ritual advances a step. Let the players see the consequence of the Threat they handed you.

• Checkpoint: Threat should change the fiction at least twice per session.
• Common mistake: treating Momentum as a scoreboard instead of a resource to spend.

Step 5: Escalate from investigation to horror

A Secret War RPG scenario works best when the mundane threat and the Mythos threat overlap. Start with human antagonists, then reveal that something older is pulling the strings. The first mission should include one moment where the players realize the rules they understood no longer apply. That is the turn from spy thriller to cosmic horror.

Do not over-explain the horror. Describe what the agents see, hear, and smell, then let them draw conclusions. In Achtung! Cthulhu, the tension comes from soldiers trained for a normal war meeting something their training cannot solve. Keep the reveal brief and let the players react.

• Checkpoint: the horror reveal should force a choice, not just a fear check.
• Common mistake: revealing the Mythos too early and losing the spy-thriller texture.

Step 6: Close the operation and set up the next one

End the mission with consequences. Did the agents complete the objective? What did it cost them? Did they leave evidence, lose an ally, or bring something back they should not have? Write down two or three loose threads and use one of them as the hook for the next session. That is how a one-shot becomes a campaign without forcing it.

Give each player a moment to describe what their agent does after the dust settles. Debrief scenes are where character creation pays off, because players show you what they care about. Note those answers and build the next mission around one of them.

• Checkpoint: end with at least one unanswered question the players want to chase.
• Common mistake: wrapping everything up so neatly that there is no reason to play again.

First mission checklist

1. Read the mission once, then outline three scenes: Read the full mission or starter set adventure before the session, then write down only three beats: the briefing, the investigation, and the confrontation. Keep the outline on one page so you can improvise between scenes. Checkpoint: if your outline is longer than one page, you are over-preparing for a first session.
2. Hand out or build agents in twenty minutes: Use pre-generated agents for the first mission if anyone is new to 2d20, or run quick character creation where each player picks a wartime background and one clear specialty. Do not spend the first hour on build optimization. Checkpoint: every agent should have a reason to be on this mission and one thing they are best at.
3. Open with a decision, not a briefing: Give the squad their objective and cover identities, then immediately ask how they approach the first obstacle. Let the players choose the entry point so the mission feels like theirs from the first minute. Checkpoint: the players should be making a meaningful choice within the first fifteen minutes.
4. Track Momentum and Threat out in the open: Use a visible tracker or note on the table so everyone sees the pool grow and shrink. Spend Threat at least twice during the session to show that complications have teeth, and remind players they can spend Momentum for extra dice or information. Checkpoint: if Threat never changed the fiction, you waited too long to spend it.
5. Reveal the Mythos once, then let the players react: Pick a single moment for the horror turn and describe it in sensory terms without explaining the cosmology. Let the agents decide whether to fight, flee, or bargain, and let their choice shape the rest of the mission. Checkpoint: the reveal should create a decision, not just a dice roll.
6. Debrief and write down two loose threads: After the mission, ask each player what their agent does next and note the answers. Pick two unanswered questions from the session and use one as the hook for your next operation. Checkpoint: end the night with a reason to come back, even if the objective was completed.

Products that help at the table

• Ruins of Symbaroum: Gamemaster's Guide: A 200-page Gamemaster's Guide for the Ruins of Symbaroum line, which brings the Symbaroum setting to the 5th Edition OGL ruleset, with inspiration, guidelines, and optional rules for designing adventures and running sessions. If your group already plays 5th Edition and wants a dark fantasy companion alongside your Achtung! Cthulhu nights, this shows how another Modiphius-adjacent setting structures GM advice and optional rules.
• Ruins of Symbaroum: Gamemaster's Screen: A Gamemaster's screen and adventure booklet for the Ruins of Symbaroum line, using the 5th Edition OGL ruleset, with the included adventure tied to the Ashurani dynasty. A screen plus a short adventure is a practical model for any first session: quick reference on your side of the table and a ready scenario to run.
• Fallout: The Roleplaying Game - Map Pack 1: Vault - Fantasy Grounds (VTT): A Fantasy Grounds VTT module for Fallout: The Roleplaying Game that includes 8 immersive battlemaps for a Vault-Tec vault; upon purchase you are emailed a product key to activate on Fantasy Grounds. If your group plays online, this shows how Modiphius handles virtual tabletop modules and product keys, which is useful when deciding whether to run your first Achtung! Cthulhu mission in person or over a VTT.

Your first Achtung! Cthulhu 2d20 mission is a short operation, not a campaign launch. Prep three scenes, hand out agents fast, keep Momentum and Threat moving, and let one horror reveal do the heavy lifting. Run it once, debrief honestly, and build the next mission from whatever your players cared about most.