After a surreal lecture on separating allied parachutists from German ones, the platoon is ordered to pick up a stranded U-boat crew. Wilson feels live hand-grenades are too dangerous for his hothead mates and acts accordingly. As HQ's armed escort is late, the Kriegsmarine captain plays mind-games by drafting a reckoning 'list', then takes 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 group, and the platoon organise 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.

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 everyone else already seems in on the secret. Alas, a regular train breaks down before the royal train, and a pills mix-up incapacitatee its staff. The platoon's ill-considered rescue attempt soon devolves into a potential real disaster.

Mainwaring is determined that his platoon should earn the full quota of a dozen stars in a wacky test weekend. Captain Ramsey is in charge and increases the psychological pressure. The intel Wilson hears from another platoon works against them.

When it becomes known an uncle's death granted Wilson to inherit an Honourable Aristocrat title, all Walmington-on-Sea flatters and woos him... except Mainwaring, whose jealous envy is all but noble. Things worsen when it's suggested he should let his honourable sergeant do the honors when the town is to honour a Soviet war ally visitor with the 'freedom' in the form of a key.

During a nightly patrol in terrible weather, the platoon run out of rationed petrol for Jones's van, so they spend the night in what they initially believe is an abandoned house. There, a drenched Pike must undress and put on a heraldic garment and, after an accidental fire complicates the hilarious sleeping arrangements all wet again, a bear rug.

Whilst Mainwaring is in hospital, Wilson is in charge. Following Walker's speedy departure 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.