Agatha Christie's Partners In Crime

On a train from Paris, Tommy and Tuppence meet an agitated young woman who mysteriously disappears. Tuppence is determined to find her. Major Anthony Carter, Tommy's uncle who works for the "Third Floor," a branch of British military intelligence, warns them off. But soon the pair is searching for the woman, a secret recording, and a Soviet hit man named Brown.

Tommy is mistaken for a wealthy mastermind who's working with Brown's violent, criminal gang. Tuppence takes a job as maid to Rita Vandemeyer, a faded soprano with ties to Brown. Vandemeyer receives a package from Brown, Major Carter is no help at all, and the Beresfords work to maintain their cover in the face of increasing peril.

With Tommy's cover blown, the gang gives him an assignment: steal a file from the Third Floor or risk the life of his young son, George. Tommy gets the file with help from Tuppence. The Beresfords race to foil a plot that threatens the British government.

There's a leak on the Third Floor, and Tommy is the only man Major Carter can trust. Carter sends him on a mission so secret he can't even tell Tuppence: find a missing British scientist, a nuclear bomb, and a Soviet spy code-named N.or is it M? Tommy goes in search of the kidnapper, but Tuppence is two steps ahead of him.

When their prime suspect turns up dead, the Beresfords look elsewhere for the bomb thief. Tommy thinks it's Carl Denim, a beatnik who's flirting with Tuppence. Tuppence thinks it's the glamorous Mrs. Sprot, who has her eye on Tommy. Tommy lets his guard down and ends up in trouble.

Tommy finds the missing scientist, but both are held captive, and the agent's identity is still unknown. Luckily, the scientist hid an important key to the bomb before his capture. Tuppence comes to the rescue, and together she and Tommy attempt to retrieve the key, but danger lies in wait. The Beresfords turn to Carter for help in devising a risky plan to save thousands of innocent lives.