A violence-prone city cop, Jim Wilson (Robert Ryan), has punched one too many crooks because of his hate for all the lowlifes in the city. Jim brutalizing suspects on the flimsiest of reasons makes his superior send him upstate to cool off and help catch a murderer. The father of the victim, Walter Brent (Ward Bond), is on the chase to catch the man who killed his daughter and begrudgingly lets Jim help him.
On the haunt for the killer, Jim stumbles upon the house of a blind woman, Mary Marlden (Ida Lupino), and finds himself falling in love with her even though her brother, Danny, is the killer.
The film asks if a hateful, lonely man can be redeemed through love.
On Dangerous Ground displays the following tropes:
- Ax-Crazy: Danny Marlden kills because he’s nuts.
- The Chase: Jim and Walter chase Danny through the woods, on a car during a snow storm, and finally, up a cliff.
- Dark and Troubled Past: Eleven years on the force has shown nothing but decay and ugly human interaction to Jim, so he ends up believing all people are horrible.
- Disabled Love Interest: Mary is blind.
- Don't You Dare Pity Me!: Averted: Mary is surprised that she doesn’t have to say this to Jim because she can hear it in his voice; he doesn’t pity her.
- Establishing Character Moment: The film begins with various vignettes about Jim’s daily routine: finding underage drinkers, fighting criminals, getting information out of various sources, not caring for the murder of an informant, and violently beating any criminal that crosses his path.
- Genre Shift: The first half of the movie plays like a regular film noir, but the mid-to-end is a bit more of a romance with a dash of noir.
- Hidden Depths: Who thought an embittered cop who isolates himself could love deeply?
- Insane Equals Violent: Danny suffers from some severe mental illness, and as a result, he is also extremely dangerous.
- Jerkass: Walter. It’s reasonable that he’s upset for the murder of his daughter and wants to catch the killer, but he wants to do this by any means necessary. He wants to kill Danny with his own gun and ignore due process. Additionally, he doesn’t realize at first that Mary is blind, and so when he does find out, he's almost smacks her in the face just to make sure, but Jim stops him.
- Loners Are Freaks: Jim wants to be alone and likes to be away from all the filth of the city. But people need love!
- Love Redeems: Jim’s harsh past can be forgotten and forgiven with love.
- No-Holds-Barred Beatdown: Jim’s style of policing. He sends many of his victims to the hospital.
- * Rousseau Was Right: The end of the film suggests this trope with Jim and Mary falling into each other’s arms and kiss.
- Save the Villain: Jim promises Mary that he’ll try and save Danny and send him to an institution instead of jail. He fails to do so.
- Would Hit a Girl: Walter almost hits Mary to make sure she’s blind, but is stopped by Jim.
- Why Did You Make Me Hit You?: Jim says this almost word-for-word when he's just about to beat up a criminal:Jim: I always make you punks talk! Why do you make me do it?