The crew encounters an abandoned ship, the "Leviathan", which is buried in the middle of an ice planetoid. In it, they find the frozen body of Caroline Carmen, one of Lister's former crushes. She is taken on board the "Starbug", where the crew attempts to thaw her out, but they are unable to melt the ice. That night, Carmen defrosts of her own accord and turns out to be in an advanced state of decomposition. She attacks Lister and spits part of her jaw and tongue down his throat, infecting him with Epideme, an intelligent virus (with an annoying personality) that was supposed to cure nicotine addiction, but in practice kills its victims within 48 hours, then reanimates their corpse to find a new victim to transfer itself to.