One player controls the human crew of the CFS Quicksilver, a small scout starship on a failed exploration mission whose crew inadvertently brings a hostile life form on board. The other player controls the protean creature in its efforts to survive. Eight humans, some with firearms and fabricated gadgets, hunt the monster. The alien has speed, hidden movement, and the ability to evolve. The alien is outnumbered, but generally more than a match for a human if it can separate one from the group. Tension for the human player derives from not knowing when and where the creature will strike. Tension for the alien player derives from being outnumbered and under constant pressure to run and hide.
The game takes one to two hours to play.