US Intelligence Agent Mark Fannon (Robert Wagner) is sent to Tokyo on a routine courier mission but soon uncovers communist George Underwood's (Edmond O'Brien) plot to assassinate the American High Commissioner (Larry Keating).

While there he meets Welsh receptionist Tina Llewellyn (Joan Collins), in whom fellow agent Tony Barrett (Ken Scott) has a romantic interest.

An attempt is made on Mark's life in a steam room and his local contact, Nobika, is assassinated.

[7] 20th Century Fox, which made the original Moto movies starring Peter Lorre, bought the film rights to the story in March 1956, prior to publication.

[8] Sam Engel was originally going to produce and William Holden and Jennifer Jones were mentioned as possible stars.

[11] Cinematographer Charles G. Clarke made expansive use of location shooting in Kyoto, a sacred Shinto city which was only lightly bombed in World War II and taken off the nuclear bombing target list (from its original top listing) due to the efforts of Henry Stimson, who argued for the preservation of its cultural assets.

Actor Ken Scott was injured in a scene when Edmond O'Brien shot a prop gun at him and a blank cartridge hit his face.

[12] Fox was so impressed with ten-year-old star Reiko Oyama, the studio signed her to a long-term contract.

The Chicago Tribune review praised the location photography but said the film "starts suspensefully, but ends limply.

"[16] Breen and Resich were later reported as working on another film for Wagner, The Far Alert, about NATO naval flyers.

A year after the movie came out Marquand told The New York Times that: Mr Moto was my literary disgrace.