The Diamond is a 1954 British film noir crime film directed by Montgomery Tully/Dennis O'Keefe (see Production section, below) and starring Dennis O'Keefe, Margaret Sheridan and Philip Friend.^[1] It is based on the 1952 novel Rich Is the Treasure by Maurice Procter. It was released by United Artists in Britain and in America, where it was known as The Diamond Wizard.

It is notable for being Britain's first 3D film, though according to the British Film Institute, it was shown in 3D only once, on 13 September 2006 in Hollywood.^[2] Despite the 2006 showing the film was listed on the BFI 75 Most Wanted list of lost films.^[2] The 2D film, however, is not lost and can be viewed on Amazon Prime while the restored 3D version was released on Blu-Ray in November 2022.

After a gang pulls off a heist to acquire freshly minted dollars, American Treasury Agent Joe Dennison pursues their trail to London. With the assistance of a Scotland Yard detective, he attempts to break a racket involving the production of synthetic diamonds.

The film was shot at Walton Studios with location filming taking place around London.^{[citation needed]} The film's sets were designed by the art director Denis Wreford. It was produced by the independent British company Gibraltar Films for release by United Artists.

There is conflicting information about who directed The Diamond. According to the British Film Institute website the British release credited British B-picture veteran Montgomery Tully as director, while the US release credited the film's American star, Dennis O'Keefe.^[2] However, the US print viewed by the reviewer of the American Film Institute Catalog of Motion Pictures credits Tully,^[3] while a YouTube video with the opening credits of a print bearing the British release title credits O'Keefe.^[4]

Monthly Film Bulletin said "The deeply involved plot is strewn with red herrings to such an extent that the film becomes more baffling than entertaining, and never rises above commonplace 'B'’ picture level. The Diamond was originally shot in 3-D, but the version shown is flat."^[5]

Kine Weekly said "The picture, originally made in 3-D, very nearly talks itself to a standstill during the early stages, but allows no grass to grow under its feet as it approaches its vivid pyrotechnic climax. Flames lick the good and the bad lads, and few will resist cheering when the rescue party puts in an appearance and the villain is consumed in the inferno. The leading characters display admirable composure in the most testing circumstances, and the stout portrayals of Dennis O’Keefe, Philip Friend and Margaret Sheridan as Joe, McClaren and Marlene, do much to mellow the rough stuff. Authentic Scotland Yard detail, too, acts as a cushion. In a word, “The Diamond ” should cut some ice with the crowd, if not the intelligentsia."^[6]

In British Sound Films: The Studio Years 1928–1959 David Quinlan rated the film as "average", writing: "Intricately developed thriller, though only the end is exciting. Originally made for 3D, but shown 'flat'."^[7]

Leslie Halliwell said: "Leaden cops-and-robbers which went out on the bottom of the bill instead of being shown in three dimensions."^[8]

The Radio Times Guide to Films gave the film 2/5 stars, writing: "A rare UK venture into 3D, this crime programme filler was shot in a process called Spacemaster. ... Mostly shown in its flat format, the film was jointly directed by its star and Montgomery Tully, who was something of a dab hand at atmosphere-free mysteries."^[9]