Waring and Bingham are on night duty in the emergency room, with sole patient Nobby Watts, when a sailor who has returned from Asia checks in - with all the symptoms of small-pox. Having rung the Medical Officer of Health to report the outbreak, the two doctors panic as they are bitten by the sailor's pet mouse and accidentally break the radiator, causing a flood. Next day it is revealed that the sailor had chicken pox, not small-pox, but the medics have to go into isolation since they were bitten by a - possibly rabid - mouse.