A malfunctioning skutter runs amok and rewires Red Dwarf's ship circuitry, producing 2,000 wiring faults and making the whole ship a gigantic booby trap. When Lister (Craig Charles) orders a milk shake and a crispy bar from one of the snack machines, he inadvertently triggers off the ship's self destruct countdown. As the auto-destruct can only be over-ridden by a senior officer, who are all dead, Kryten (Robert Llewellyn) performs a mind-swap. The mind of Executive Officer Carol Brown is temporarily placed into Lister's body so she can voice-activate the shut-down procedure but the plan fails and the auto-destruct sequence continues. When the countdown reaches zero Lister's milk shake and Toffee Crispy bar (The actual product was a Toffee Crisp) are dispensed from the food machine.
After the crisis is resolved, it gives Rimmer (Chris Barrie) an idea. He convinces Lister to swap bodies with him. He will be able to enjoy the benefits of having a tangible body again for two weeks, while he exercises and gets Lister back into shape. However, he is unable to resist the pleasures he has been denied for so long, and eats, drinks, and smokes so much that Lister, appalled, demands his heavily abused body back after just one week.
Rimmer, enlisting Kryten's reluctant help, chloroforms Lister and reacquires his body. In Lister's body, Rimmer then absconds in Starbug with a full freight of junk food. Lister, with Cat (Danny John-Jules) and Kryten, give chase with Blue Midget causing Rimmer to lose concentration and crash into a rocky planet. Rimmer is forced again to give Lister's body back, but later Rimmer walks into Lister's sleeping quarters looking strange. It is Cat and he says that Rimmer has stolen his body. Just then Rimmer, in Cat's body, turns up carrying a heaping dinner plate and assures his crewmates that it will be for just one night... or maybe until Thursday.