Tenshuu Yashiro is on death row for killing the four men who assaulted his girlfriend and then killing her as well. On the day set for his execution he is offered a swap: die on schedule, or submit to an experiment. He takes it, and he and another condemned man, Gondo, are shut in a comfortable room with food, drink and nothing to do but wait. What the people watching want to see is how a parasite said to feed on murderous intent takes to hosts like them.