Saddled with amnesia, Yuuri awakens on an interstellar cruiser drifting through space. Unfortunately, a lack of memories is the least of Yuuri's problems. Among the four other crew members is a Gnosia: a Gnos infectee whose goal is the eradication of humanity. The Gnosia appears human in all other respects, so the uninfected have little choice but to vote on whom they suspect to be the enemy, hoping to neutralize the Gnosia by putting them into cold sleep. If the Gnosia survives the vote, they will eliminate one crew member during the cruiser's following warp, when only the Gnosia remains conscious.

Voting quickly proves to be an unreliable strategy, and Yuuri is left one-on-one with the Gnosia. Just when all hope seems lost, time seemingly loops back to when Yuuri first awakened. With each time loop, however, conditions aboard the ship change—neither the size of the crew nor the members' identities remain constant. Trapped in both time and space, Yuuri must figure out how to escape the loops and save humanity from the Gnosia.