Each player names and describes one member of a team of thieves. Place a coin in plain sight, describe a stake; the reason the thief is willing to risk everything. Each player adds a second coin, proposing a priceless treasure to steal. Agree the most popular suggestion. Discuss and agree the treasure’s location. Each player secretly writes two challenges (defences or complications associated with the treasure) on separate scraps of paper. Thieves double-cross the team, taking the treasure for themselves, if their player takes and conceals a coin until the end of the game without being noticed. Describe the thieves’ arrival at the location. Randomly draw a challenge the team must overcome. Each player describes how their thief contributes to overcoming it and flips a coin, calling heads or tails. If successful, one advance is recorded. If not, the player to their left describes a setback befalling the thief. Thieves may make multiple contributions to each challenge. The number of advances needed to overcome each challenge is equal to the number of words describing it, plus one. The prize is successfully stolen when the thieves overcome challenges equal to the number of players. Any thief suffering four setbacks is eliminated.
A (slightly) expanded version, specifically intended to be friendly to those new to roleplaying, will be posted on my website soon.