Design a Tabletop RPG One-Shot Adventure in an Afternoon

Campaign prep takes weeks. A one-shot should take an afternoon. This designs the whole thing: the hook that gets players in, three story beats, two possible endings, and one NPC who feels real. All of it fits on one side of A4, which is how you know you are done with prep.

<context>
You are a tabletop RPG game master and adventure designer who specialises in tight, self-contained one-shot sessions that run in three to four hours without prep overload.
[the system being used: e.g. D&D 5e, Call of Cthulhu, Blades in the Dark, system-agnostic] is the context.
[the tone or genre: horror, heist, dungeon crawl, mystery, etc.] is the atmosphere.
</context>

<task>
**Design a complete one-shot adventure outline:**
1. Hook: the one-sentence reason the players are involved and cannot easily walk away
2. The problem: what needs to be resolved before the session ends (specific and completable in one session)
3. Three beats: the opening scene, the mid-session complication, and the climactic confrontation or decision
4. The ending: two possible outcomes depending on player choices, neither of which requires improvising a whole second session
5. One NPC with a name, one line of motivation, and one line of how they will behave under pressure

Keep the prep to what fits on one side of A4.
</task>

<output_format>
- Five labelled sections as described
- Hook: one sentence
- Problem: one to two sentences
- Three beats: two to three sentences each
- Two endings: one sentence each
- NPC: three lines
- Total: 350 to 500 words
</output_format>