This is one of Alfred Hitchcock’s best films, based on a popular stage play by Frederick Knot, who also wrote the script for the film.
Like its even better immediate successor, Rear Window, Dial M for Murder is set almost entirely in a single apartment. Both films also star Grace Kelly as a wealthy and beautiful woman. But while Rear Window is character-driven, has some interesting insights about human relationships, and takes place in Greenwich Village, the emphasis of Dial M for Murder is on the plot and a small handful of individuals, and the setting is London.
Kelly is married to former tennis pro Ray Milland. Robert Cummings is a visiting American mystery write who had an affair with her a year before. Hitchcock regular John Williams (the British actor, not the composer) plays a police inspector, and character actor Anthony Dawson is a con man blackmailed into committing murder. Everyone is quite good. I don't want to say more about the plot because it’s full of entertaining surprises I wouldn’t want to spoil. For the same reason I'm omitting a trailer, though you can find one easily enough on line.
I think this was the only Hitchcock film produced in 3D, and he made good use of it in his compositions, though like most good 3D movies it’s fine in 2D as well (which is how I saw it). In fact, the only notable artifact of its having been a 3D movie is the fact that it has an intermission despite running only an hour and 45 minutes.
Even the largest projector reels in the 1950s held less than an hour’s worth of film, so a movie theater had two projectors in the booth, permitting the projectionist to switch seamlessly from one to the other at the end of each reel. But high-quality 3D projection required using both projectors at the same time in perfect synchronization, one for the left-eye image and one for the right, with polarizing filters on the projector lenses and corresponding ones in spectators’ 3D glasses. This necessitated a pause between reels to reload the projectors, hence the intermission in Dial M for Murder.
There was an alternative, cheaper single-projector process involving not polarization but different colors for the left and right images, but big-budget 3D movies then as now used polarization.
(Later advances allowed projecting both polarized images from a single projector and reel of film. Today 3D projection is digital, and the filters employ helical rather than linear polarization.)
Another consequence of shooting in 3D in the 1950s was that the camera rig would not allow extreme close-ups. Since Hitchcock wanted to show a very tight shot of a finger dialing a telephone at one point, the prop department had to build a giant telephone dial and a giant finger. They did so good a job that it’s hard to tell it isn’t real.