General Burkhalter and Dr Felzer of Research 49 are visiting Klink. Felzer comes directly from Hitler and is working on a top secret matter that he wants to discuss with Klink. He is worried about security and bugs (and of course his fears are well-founded, as Hogan and Co are listening in), but Klink assures him that it is safe. Felzer tells Klink that he has been chosen for a top-security assignment involving the highest security project in Nazi Germany. But then he decides to discuss it further in Burkhalter's car. Le Beau is smuggled into the trunk of Burkhalter's car to listen in.
Later, Le Beau reports to Hogan that it is atomic research in a specially built laboratory, but Felzer did not say where it was. Klink is in charge of security, having been chosen because of his record, and will get a promotion. This means a new commandant, which could spell the end of their operation. But first they have to deal with the research plant.
Hogan goes to work on Klink. He finds Klink packing his belongings and feigns dismay as he wanted Klink to judge their upcoming rumba contest. He asks Klink for his new address so he can write, but only gets an unhelpful PO Box number. Le Beau tries to pump Schultz using strudel, but only finds out that Schultz is leaving as well. Schultz tells Le Beau that he should know by now that he knows nothing.
When Klink and Schultz are taken on their inspection tours of the facility, Hogan and Co monitor the mileage, which narrows the location down to a 12-mile radius. The discuss it with Carla of the Underground, but find nothing to work on. So they decide to have another go at Schultz, but this time using a truth drug. They arrange to have London drop it to them, and then Dr Schneitzler (Newkirk) administers the drug to Schultz on pretext of inoculations for the transfer. The yields nothing definite about the location; the only clue is Flenzheim potatoes being delivered to the facility. Carla goes to check out the possible Flenzheim connection with her contacts.
This time, they come up with the answer: it is an underground installation located underneath a bombed-out factory. As it is underground, an air raid will be of no use, so they must destroy it themselves. Carla tells them that the guards take produce from neighbouring farmers and only pay them in vouchers. They disguise themselves as farmers, conceal bombs in Flenzheim potatoes and take them along to the facility along with some other produce. The guards snap up the produce at the point of a gun; Hogan had protested that the produce was meant for Stalag 13. To Hogan's dismay, the guards force Le Beau to take the produce in, which means he will be blown up as well. He orders Carter to throw a grenade down the ventilator as a diversion while he goes in for Le Beau. But just then, an officer throws Le Beau out and puts the guards on report for breaking regulations by allowing him in there. He then orders Hogan and Co off. They do, and are soon watching the facility blow up.
Back in camp, Hogan and Co are about to say goodbye to Carla when Klink drops in. They have to hide her quickly. Klink says that his transfer has been cancelled because some farmers blew up the post. Now that he is staying, he can judge the rumba contest. So Hogan and Co now have to organise one.