Adapting a play into a film requires more specialist skills than transforming a book into a movie. A book either needs considerably trimmed (example, The Detective) or the requiring a complete overall (as with Blindfold). It’s much harder to muck around with a play which has usually been well-honed, edited down night after night, from a run on the stage. The main decision the writer charged with the adaptation has to make is a tricky one – whether to open it up or not. Can a play, especially a thriller, sustain the tension it achieved on stage without additional elements – and therefore appear “stagey” on film – or must it be expanded in the hope of generating greater tension or ambiguity, making characters more sympathetic or clarifying the plot. The story in both play and film concerns top lawyer Simon Crawford being arrest for murder.
Jack Roffey, adapting his own play, decided the original needed opening up. The play’s structure consisted of two acts, each containing two scenes. The first scene lasted 21 pages, scenes two and four 23 pages each, while scene three is considerably shorter just 12 pages. So, except for the third scene, the play’s rhythm is consistent. And while this might look as if most scenes last 20-plus minutes, an inordinately long time to sustain rhythm on the screen, there are lot of moment where various characters go offstage to concentrate action between fewer characters, thus heightening tension or creating character conflict.

A lot of information that was imparted purely via dialogue in the play transforms on screen into a series of extra scenes. This is especially true at the beginning. The movie’s opening scene, set in a court and concerning the trial of a brothel-keeper, was not in the play; it was dealt with in passing at the beginning of the play, as a character reporting on the outcome, albeit that some of the reported speech became dialogue in the film. It was probably felt that the movie audience had to be introduced right away to a courtroom since the play’s opening scene takes place entirely outside the courtroom, in the offices of the leading character Simon Crawford (Ray Milland). The play begins in the present and the back story, that Crawford is widowed, recently lost his daughter in a hit-and-run traffic accident, and suffered a nervous breakdown as a result, is dealt with as exactly that – events from the past. The film puts them in the present. We are shown the daughter, who clearly has a strong relationship with her father, we hear the accident (which occurs offscreen), witness Crawford’s unravelling and the murder that forms the core of the story. And we are also treated to some additional scenes, not in the play, including an initial police investigation.
The upshot is that it takes 25 minutes for Crawford to be arrested. Compare that to the play. He announces his imminent arrest within the first five minutes. For pure audience shock the play holds the upper hand. I’m not sure the film ever matches that moment. Pre-arrest, in the film, Crawford’s erratic behaviour and hospital confinement add to a sense that he might be unhinged or, in classic film noir, feeding the audience a line. His state of mind is complicated by making visual some incidents that were just verbal in the play.
There are three major departures from the play. The first was the introduction of a private eye whom Crawford takes by the throat in frustration at the gumshoe producing no results. This suggests early on that Crawford is capable of violence. But it also causes a complication. In the play there is only one main private eye, name of Armitage, whose evidence proves key in the case against Crawford, but he is missing and in fact never appears. Apart from testifying to Crawford’s murderous inclination the introduction of this other private eye, named Rosen, makes little sense. The second is to bring quicker to the fore the involvement of junior lawyer Sheila Larkin (Sylvia Syms in the film). In the play she takes over his defence when her senior quits on a point of principle but in the film it is almost from the start.

The third development also involves Larkins. But I’m not sure this one works in building up Crawford-Larkins into a potential May-December relationship. In the play it seems more obvious that Larkins is a daughter substitute rather than a potential love interest but the film adds an additional scene where she brings celebratory goodies to the lawyer and her demeanor suggests sublimated ardor. The way director Ray Milland uses looks between the pair and an occasional touching of hands makes the alternative more obvious.
You could argue that the film could have simply had Crawford arrested in the first five minutes but that would have necessitated police interrogation. The device brilliantly used in the play of imminent arrest would have worked in the film, I believe, and made for a more explosive start, and then either sticking with the play structure or dealing with the backstory in flashbacks.
It’s worth noting that plays on the page look far more intense than screenplays. There is nothing but line after line of dialogue whereas a screenplay always has cuts or directions to interrupt the flow of material. Dialogue, of course, being what a play relies upon more than the camera, Roffey, as the adaptor, was lucky in having so many choice lines at his disposal. Ray Milland, in his role as director, unfortunately, was not able to add atmospheric heft.