After a surreal lecture on telling allied parachutists from German ones, the platoon is ordered to pick up a stranded U-boot's crew. Wilson feels live hand-grenades are too dangerous for his hot-head mates and acts accordingly. As HQ's armed escort is late, the Kriegsmarine captain can first play mind-games by drafting a reckoning 'list', then take Hodges hostage.
After two and a half years the Americans have finally decided to enter the European war. Walmington-on-Sea gets to welcome an advanced party. The platoon organizes a welcome party. Given the rations and misunderstandings on both sides, however, tensions run high. Still, the alliance is vital, so fences must be mended from both sides.
Captain Mainwaring gathers his troops for the secretive reading of top-secret orders, concerning the passage - no actual stop - of the royal train. The mood darkens when everybody else seems in on the secret. Alas, a regular train breaks down before the royal train, and a pills mix-up knocks out its staff. The platoon's ill-considered rescue attempt soon turns into a potential real disaster.
Vain Mainwaring is determined that his platoon should earn the full quota of 12 stars in a wacky test weekend. Captain Ramsey is in charge and increases the psychological pressure. The information that Wilson heard from another platoon works against them. Meanwhile the warden and the verger follow them because Jones' van still has an onions consignment for Hodges' grocery shop, which suddenly gains another importance.
When it becomes known the death of an uncle caused Sergeant Wilson to inherit an Honorable aristocratic title, all Walmington flatters and woos him. All except Mainwaring, whose jealous envy is all but noble. It gets worse when it's suggested he should let his honorable sergeant do the honors when the town is to honor a Soviet Russian war ally visitor with the 'freedom' in the form of a key. Vladimir in turn hardly honors his hosts, except one.
During a nightly patrol in terrible weather the platoon runs out of rationed petrol for Jones's van, so they decide to spend the night in an at first sight abandoned house. There Pike, who got drenched, must undress and put on a heraldic garment and, after an accidental fire complicates the hilarious sleeping arrangements all wet again, a bear rug. Frazer's ghost stories seem to come to life with footsteps once everybody is asleep, but it's just captain Cadbury, a military dog school administrator who lives here with the hounds in training. In the morning friendly ...
Whilst Mainwaring is in hospital Sergeant Wilson is in charge. Following the speedy departure of Walker back to London, leaving only a note behind, Wilson decides to make up the platoon's numbers by allowing the vicar and the verger to join. Needless to say both of them are hopeless and the verger causes trouble by hitting a cheeky young lad who turns out to be Hodges' nephew. These new recruits are not in the Home Guard for very long.