Directed by Anatole Litvak, with a screenplay co-written by John Huston, this above average comedic crime drama featuring Edward G. Robinson, also stars Claire Trevor and Humphrey Bogart, among several other Warner Bros. stock players.
The titled Doctor (Robinson) is a respected Park Avenue physician, a frequent guest at high society parties, who personally engages in thievery as research for a book that he hopes will provide insight into the physiology of the criminal, and "his" mind. During this quest for knowledge, Dr. Clitterhouse associates with the city's highest stakes fence Jo Keller (Trevor) and "her" gang, led by "Rocks" Valentine (Bogart), while trying to avoid capture by his acquaintance, Police Inspector Lewis Lane (Donald Crisp). The performances by its three leads (Robinson, Trevor, & Bogart) are particularly good.
Clitterhouse has just beaten a member of Rocks's gang to a safe full of jewels at a Park Avenue party he's attended. After checking on a patient's condition by phone, he even calls the police and attends to the "innocent" criminal who was captured and shot in the confusion. Naturally, he avoided Police Inspector Lane's suspicion, under whose nose he escapes with his bounty on his way to surgery (on Thurston Hall's character, that appears again later). His nurse (Gale Page) discovers the jewels and learns from the Doctor that he is doing research - recording his own physical reactions before, during, and after committing these crimes (four, so far) - in hopes of writing an insightful book about it for the benefit of science and/or law enforcement. Because she's obviously fond of her employer of many years, whom she feels is just overworked, she agrees not to tell anyone.
In order to learn more, Clitterhouse and nurse even visit his acquaintance, Inspector Lane, to find out what he should do next. The Inspector freely shares that a jewel thief will try to pawn his take and even gives Clitterhouse the name of the one most likely able to handle the caliber of stuff that's been stolen. So, Clitterhouse goes to the Sequin Hotel, which is owned by the pawn named Keller, whom he is surprised to find out is a woman named Jo.
One of the film's best scenes involves Clitterhouse's "introduction" to the gang of thieves with which Jo is associated. His visit just happens to coincide with the appearance of Rocks and a raid on her hotel. Clitterhouse quickly hides the jewels in a bowl of pretzels and then proceeds to "dress down" police Lieutenant Ethelbert Johnson (Robert Homans); his logical approach to the situation helps him avoid giving his name and endears him to Jo and the gang which includes her bodyguard Butch (Maxie Rosenbloom), Okay (Allen Jenkins), and Tug (Ward Bond) among others.
Rocks, who'd been hiding in the closet, was not so impressed and/or immediately recognizes the threat to his leadership. Clitterhouse and Jo discuss a partnership, his brain with her people, which then enables him to study a larger population of criminals' reactions before, during and after their crimes. He pretends to go abroad while he sets up shop at a studio where the gang pretends to be musicians when they're not carrying out the crimes that the Doctor has planned. Mild humor and symptoms, such as Okay losing his voice when he gets nervous, are incorporated while Rocks bides his time and waits for the proper moment to regain the power again.
That opportunity comes when Clitterhouse plans a large fur heist. Jo, who's fallen in love with the Doctor, suspects that Rocks may be up to something and sends her heavy Butch, for the first time, on the job. Sure enough, Rocks seizes the chance by locking Clitterhouse in the safe, which he'd opened by hand, on his way out. However, because Rocks also turned up the safe's cooling system, the Doctor's respiratory system was lowered long enough for Butch to torch the safe open again, and before he'd run out of oxygen.
An anxious Jo and company wait at the studio for Clitterhouse's return, but just as Rocks is being questioned, Butch and the Doctor arrive. Without explicitly exposing Rocks, Clitterhouse decides that his work is done, that Rocks can have his gang back, and gives the boys their final payoffs before leaving. A cheap plot device involving the phone is used that enables Rocks to track the Doctor, heretofore known to the gang only as "the Professor", back to his Park Avenue office.
Jo soon follows but is too late to warn Clitterhouse before Rocks has him at the point of his gun. Rocks confiscates the Doctor's research which he protests is full of incriminating information. He then tells Clitterhouse that he likes the Doctor's setup and thinks, with Clitterhouse's social contacts, that it will be the perfect base of operations for future thefts. Trapped, Clitterhouse's warped mind rationalizes the need for yet another chapter for his book, concerning the ultimate act - murder, which he proceeds to commit by putting a specialized poison in Rocks's drink.
Even though, out of love, Jo tries to confess to Inspector Lane about Rocks's murder, another couple of cheap plot devices are employed which enable Lane to arrest Clitterhouse, who had just confessed his crime to his friend and attorney Grant (Hall). Grant pleads his case as insanity to the Judge (Henry O'Neill), the jury and its exasperated foreman (Irving Bacon), against the prosecutor (John Litel).
A little hackneyed perhaps, but a perfectly logical (and amazing!) verdict is eventually rendered, which somehow got by the censors at the time (who insisted that no criminal should go free and, after all, Clitterhouse was a murderer even if it was a criminal like Rocks!) - not guilty, though the Judge does recommend that the state doctor's examine him.