On seeing his adopted goldfish get busted for stealing top-secret documents, Penfold bewails the fact he has never had a pet of his own to love and cherish. He gets his wish when Danger Mouse and Squawk discover the Baron's plans to brainwash the world's pets into becoming his personal army of slaves. They hand him the responsibility of babysitting the Baron's own pet Nero, having craftily swapped him with a robotic impersonator as a means of getting to the Baron's mind control device - The Pet Whistle!

Colonel K spins a terrifying tale about the Headless Postman - an ancient and alarmingly scary apparition. When the haunting figure of the postman suddenly appears, petrified panic reigns supreme amongst the Danger Agents, until Squawkencluck reveals herself as the postman in disguise and that the whole scenario has been a company-mandated bravery test. By remaining characteristically unfazed throughout, Danger Mouse fails the exam, which puts his job at risk, as in Squawk's words 'being truly brave means being afraid of something and still taking it on'. The gang try to scare DM, but he's fearless... until he discovers that the Headless Postman lives!