Le Beau is returning from a rendezvous with an Underground agent who is passing him vital information that could make or break D-Day. But the guards are unusually heavy and blocking his return. Hogan dispatches Carter and Newkirk to find Le Beau; they find him in the tunnel entertaining the agent, Kristina Jerrold. Jerrold has bad news for Hogan - the Underground courier system is broken, so they cannot distribute the information to the contacts, which must be done by the weekend. And Hogan figures the information must be distributed manually because radio is too risky. To add to his problems, Jerrrold is now stuck in camp (not that his men are complaining), and the extra guards will make it extra difficult to get her out.
The extra guards are explained when Klink summons Hogan the following morning. General Burkhalter had ordered them - and personal guards for the commandants - because two stalag commandants have been murdered and he fears an epidemic. So does Klink (though he tries not to show it) and asks Hogan what the prisoners think of him. Hogan takes advantage to wangle white bread and the return of a Red Cross package, but Klink persists with his question. Before Hogan can reply, Klink's new cuckoo clock goes cuckoo. Hogan laughs and says the cuckoo took the words right out of his mouth.
Then, claiming he has knowledge about antiques from his mother, Hogan examines the clock and says it is a real antique. He wants to buy it, and forces up the price to USD100.00 and the Red Cross package, which Klink accepts it. When Schultz hears, he is astonished; those clocks sell in Hammelburg for 10 marks (USD3.00), but Klink shuts him up, thinking he has made a sucker out of Hogan and made a satisfactory profit. When Hogan's men hear, they likewise think he is cuckoo; they know how much the clocks sell for in Hammelburg. But Hogan has a plan, and it involves setting up Klink in the cuckoo clock business.
The plan works; Klink is soon buying up cheap cuckoo clocks to sell as antiques and picking Hogan's brains for antique and business advice. Hogan takes advantage to get back the money and the Red Cross package. He advises Klink to send one cuckoo clock to antique dealers in various cities (where the contacts will be). But then Burkhalter arrives, and Klink does not want Burkhalter to know what he is up to. They hide most of the clocks in the guest room closet. Hogan takes five to the barracks on pretext of authentification. In reality, the information is going to be hidden in the clocks for the contacts to pick up.
Burkhalter tells Klink that another commandant has been murdered and he is staying overnight to tighten security. He will be staying in the guest room (where the clocks are hidden). Hogan sees Burkhalter as their answer to getting Jerrold out. He sends Carter and Newkirk to the guest room to wind up the clocks. When Burkhalter hears the ticking, he panics, thinking it is a bomb, and Klink will not tell him about the clocks. Hogan arrives and winds Burkhalter up further with a story that the Gestapo may have planted a bomb as they do not like generals. Burkhalter shouts for the guards and fire hoses. Carter and Newkirk bring in the hose, which Burkhalter directs towards the closet. Klink gets drenched while trying to save the clocks, which end up ruined. Meanwhile, Hogan's men smuggle Jerrold into the trunk of Burkhalter's car.
The Underground receives four of the clocks, but have to chase an antique dealer for the fifth, which turned out to be a genuine antique. Klink summons Hogan and shows him his new line of antique clocks - the statue of Brunhilde of Hammelburg. He wants Hogan's expert opinion on their value. Hogan takes a sample to the barracks, saying Le Beau is more qualified to authenticate this one.