Watch Your Stern

HMS Terrier is docked at Chatham Royal Dockyard as the officers drink in the captain's quarters and the crew receive casual yet technical torpedo lectures from Seaman Blissworth. The mood is light, but Blissworth's knowledge hints at the secret plans to come. The setup foreshadows deception and danger around the acoustic torpedo project.

An American Naval Commander visits on board to discuss plans for a new acoustic torpedo, raising the stakes for secrecy. The meeting introduces the central objective and the potential vulnerability of sensitive designs. Tension rises as the team weighs the need to protect the information.

Blissworth accidentally spills a drink on the secret plans and hangs them out to dry by a heater, swapping the folded secret plan for other plans intended for the ice unit. The heater burns a hole in the original secret plan, risking exposure. The crew scrambles to hide the damage and keep the Admiral in the dark.

The visiting Admiral is being kept in the dark while the only surviving plan sits with the American Commander en route to London. The crew and Blissworth hustle to conceal the damage and maintain the illusion of control. The whereabouts of the plan become a critical point of tension.

Blissworth is sent on a bicycle to catch up with the Commander, but he is not allowed out without a pass, so the mission fails. The bureaucratic obstacle highlights the fragility of the plan under wartime improvisation. The pursuit continues through other means as the plot thickens.

Admiral Pettigrew orders a plan to see the documents and Blissworth is transformed into a scientific expert, 'Professor Potter', complete with a glued-on beard, glasses, and a Scottish accent. He convinces the visiting Admiral that a refrigeration circuit diagram is actually a torpedo diagram. The deception relies on convincing presentation rather than substance.

The real scientist turns out to be Agatha Potter, the true expert, who phones to say she will be late. The ruse depends on her absence, and the delay increases the risk of exposure. Tension escalates as timing becomes critical to the deception.

Petty Officer Mundy is ordered to shave off the remaining whiskers, reflecting the navy's strict appearance options. The disguise relies on facial changes and the policy creates additional pressure. The crew braces for possible slips in the ruse.

Blissworth re-embodies as Agatha Potter and is collected by the Admiral's secretary for a meeting at Admiralty House. He is present when the real Agatha calls and exposes the disguise. The ruse collapses, forcing a rapid pivot in plans.

Blissworth escapes Admiralty scrutiny by accepting a ride with the returning American Commander and retrieves the correct torpedo plan. He secures the document and returns to the Terrier with the plan in hand. The recovery marks a turning point in the mission.

Back aboard, Blissworth returns the plan and changes back into his naval uniform before the Admiral arrives with the real professor. He interrupts the discussion and reveals a flaw in the current design. The incident earns him a chance to collaborate with the professor on the project.

The Admiral invites Blissworth to work with the professor on refining the torpedo design, acknowledging his practical insight. The farce gives way to serious research as they begin a cautious collaboration. The mood shifts toward measured optimism despite the chaos earlier.

When the first torpedo is fired, it turns around and blows up their own ship, delivering a comic yet catastrophic punchline. The test backfires spectacularly, underscoring the risks of espionage and improvisation. The finale leaves the crew scrambling amid the wreckage and the wrecked plan.