Flapjack makes all the citizens of Stormalong uncomfortable when he becomes friends with a rat he names "K'nuckles II" while the real Captain K'nuckles is away. It turns out that K'nuckles II has the apparently supernatural ability to infect anybody who is cruel to Flapjack with the plague by flicking its fleas on them, and, almost overnight, everybody in Stormalong but Bubbie and Flapjack himself are infected (although the original K'nuckles purposely gets infected to avoid helping Doctor Barber take care of the others). Flapjack has no choice but to send his rat friend to "Plague Island". Then it turns out that Flapjack's blood carries a natural antibody to the plague, and he is the key to the survival of the denizens of Stormalong, which explains why K'nuckles and the other infected inhabitants of Stormalong claim that they "cannot live without him". The episode ends as an infected Dr. Barber appears with a large hypodermic needle to get a blood sample from Flapjack.