Peter Chapman, an electronics professor at the Polytechnic, is followed by two MI5 agents (we find out later it's Dexter and Lewis). The agents at MI5 have had trouble figuring out how to use the technical equipment they're given for surveillance, and two higher-ups, namely Maxwell and Drummond, are impressed with Chapman's teaching credentials. So Peter is given a small incentive to join up - he's fired from his job at the Polytechnic! He interviews for the MI5 position and when they finally tell him what it's really about, he asks for a code name. Maxwell says he's been watching too many movies, but Peter is disappointed so they give him a code name: Piglet. Piglet's job is to assist in instructing the agents on how to use the equipment. Unfortunately, he inadvertently bungles a job in which Dexter and Lewis were trying to prevent Peter's supervisor from defecting to the USSR. So Maxwell and Drummond read Peter the riot act for messing up his first day on the job, but at the same tim (thetvdb.com)