At a by-election in a traditional Labour area Conservative candidate Victor Crosby astonishes everybody winning by a landslide. He's immediately seen as the new hope for the Conservatives and when Sir Greville introduces him to Alan, he appears to be even more right-wing than B'Stard. Crosby gets Alan's desk in the office and can even steal a newspaper column from Alan by spouting even more radical opinions.
At home Alan finds a stranger's glasses in his wife's bathroom cabinet. By coincidence, Sir Greville had mentioned that he had lost his usual pair. Alan decides to sabotage Crosby's career and he goes to see the competition. He promises Labour Party official Paddy O'Rourke dirty secrets from the Conservative. In return he wants a position in the next Labour government. O'Rourke is not interested at first, but then Alan shows some pictures that might embarrass O'Rourke.
In an effort to find something incriminating on Crosby, Alan looks through his desk. Piers catches him doing that and goes on about how wonderful Crosby's maiden speech was. When Alan hears that sir Greville was not present at that speech, he puts two and two together. He returns to his house and sees Sarah and Sir Greville kissing. As they retire to the bedroom, Alan looks through Sir Greville's red box.
Alan congratulates Crosby on his speech and mentions that Margaret Thatcher is a great fan of Crosby's. He even suggests that Crosby should send a Valentine card to the former PM. Because Crosby hurts his right hand on a mousetrap in his desk drawer, he has to sign the card with his left hand. Alan takes the opportunity to slip a piece of carbon paper underneath so that he gets a perfect copy of the signature. He then sends sensitive information purloined from Sir Greville's red box to the Labour Party, with Crosby's signature.
The document causes a scandal, infuriating Sir Greville. Alan offers proof that Crosby was responsible (an edited tape). He also returns Sir Greville's glasses and asks him not see Sarah any more.