Murder Ahoy

A fellow trustee returns from a surprise visit to HMS Battledore and dies suddenly, distressed by what he saw but never reveals it. Miss Marple witnesses the death and suspects foul play. A sample of the trustee's snuff is taken and later proven poisoned, triggering the investigation.

Miss Marple obtains the trustee's snuff sample to submit for analysis. The poison is confirmed, establishing a homicide motive. This clue sharpens her resolve to uncover what was hidden on the ship.

Resolving to learn what the trustee discovered, Marple visits the Battledore and decides to remain aboard for several days. She even plans to sleep in the captain's quarters, forcing him to move to the first mate's cabin. Captain Rhumstone resents her presence from the outset.

That night, Marple signals Stringer to tail the sailors who had gone ashore. He discovers they are burglarizing homes and informs Marple. Lieutenant Compton overhears and heads to warn the Captain, only to be murdered with a sword and hanged from a mast.

The investigation uncovers that the assistant matron has been killed, apparently by a poison injection. Trafalgar Day celebrations on the ship are disrupted by the turmoil. The Captain blames Miss Marple and begs Chief Inspector Craddock to get her off the ship.

Marple persuades Craddock to let the crew go ashore for Trafalgar Day, creating a window for the culprit to act unseen. She hints she will reveal the murderer's identity soon, upping tension aboard. Dimchurch is found skulking about and claims seasickness as an excuse.

With the crew ashore, Marple searches the ship for the loaded mousetrap used to administer poison. She finds it concealed in the cannon barrel, along with a large sum of embezzled money. Breeze-Connington confronts her and hints at his motive.

Breeze-Connington admits he has been embezzling the ship's funds for years and believes he was unjustly passed over for promotion. He acknowledges having committed the three murders to avoid exposure and reveals his plan to kill Marple and flee the country.

Unable to back down, Breeze-Connington draws his sword to strike Marple. She proves to be an accomplished fencer, and the duel turns against him. Stringer returns and clubs Breeze-Connington with a belaying pin, ending the threat.

The captain faces a court martial for failing to detect the embezzlement, but the board finds him not at fault. Despite this relief, he announces he must resign because of his long affair with the ship's matron and to avoid disqualifying the role. He and the matron plan to marry.

Miss Marple tells the captain that he should remain in command despite the affair, offering him a path to restore his standing. The captain and the matron embrace warmly, signaling a complicated but hopeful future.

Marple steps into a dinghy to leave the ship, while the captain and matron wave goodbye. The voyage resumes its course, and order is restored on the Battledore as officers reflect on the resolved mystery.