The plot of the movie is pretty twisty and convoluted but revolves around essentially 2 storylines, which are of course connected in various ways.
The first storyline revolves around Johnny O'Clock (Dick Powell) who runs an illegal gambling joint together with Guido Marchettis (Thomas Gomez). Marchettis is married to borderline alcoholic Nelle (Ellen Drew), O'Clock's ex-girl who still wants O'Clock but married Marchettis because he can provide her with the lavish lifestyle she wants. Nelle gives O'Clock a watch with an engraving as a gift, but he doesn't want things to get any more complicated than they already are. He drops off the watch with hat-check girl Harriet Hobson (Nina Foch) to return to Nelle. But the next morning Harriet is found dead, she apparently killed herself. The connection to the second storyline is Chuck Blayden (Jim Bannon), who's Harriet's boyfriend and wants to replace Johnny as Marchettis' partner in the gambling outfit.
The second storyline revolves around inspector Koch (Lee J. Cobb) and his search for Blayden, who is a crooked cop and wanted for several murders (which are suspected to be ordered by Marchettis). In his search for Blayden he finds the dead body of Harriet. Harriet's sister Nancy Hobson (Evely Keyes) flies into town to deal with her sister's death, and ends up falling for Johnny, who took a liking to Harriet. Blayden however turns up dead and Koch is convinced O'Clock knows more than he's willing to share.
Dick Powell is great as Johnny O'Clock with an arrogant, cocky and self-assured demeanor. He keeps everybody at bay with hard-boiled retorts, veiled insults and sarcastic quips while keeping a very suave air around him. He's not gritty and tough like Sam Spade or Mike Hammer however, which gives his hard-boiled talk a smoother and different edge. But he does also have his soft side as well, he seems fond of Harriet, and he's taken in a former delinquent as a roommate. This roommate, Charlie (John Kellogg), and him have a weird mentor/pupil-like relationship going on which might be meant to suggest a homosexual side to O'Clock', who does play it real cool, ice-cold even, around the ladies... Until Nancy enters his life, and even then he cannot help but build a brick wall around himself, despite falling for her. Evelyn Keyes ('The Prowler', '99 River Street') does a solid job with her portrayal of Nancy, the only downside is that they don't seem to really connect, there aren't any real sparkles between her and Powell/O'Clock.
In that respect, Ellen Drew is better, she gives a great performance as Nelle, who flirts a lot with Johnny, and seems to take even more pleasure in it when Guido is around, and their innuendos seem real. Lee J. Cobb ('Thieves' Highway', 'Call Northside 777') plays his usual type of role, that of a smudgy trenchcoat-wearing detective/cop with a cigar hanging from the corner of his mouth and the tenacity of a bulldog. He's solid but at the same time, it's almost a caricature part, the second you see him, you know his entire character. Not that I mind, Cobb was great at playing these types of characters. Thomas Gomez ('Key Largo', 'Macao') is pretty slimey and sleazy as Marchettis, he's fun to watch in this movie.
The movie looks beautiful, there are some great shots and the play with shadows, (cigarette) smoke, staging and lighting is impressive. At times it even looks like the visuals and atmosphere of the scene are more important than the actual story, which does make the movie hard to follow at times. But it doesn't mean the movie is slow, it's well-paced and moves along rapidly. It's highly enjoyable and I'm surprised/disappointed that this movie hasn't had a proper DVD release yet. It certainly deserves it.