Police detective Jim Wilson (Robert Ryan) attends the meeting at the beginning of his shift where the boss tells the assembled it has been two weeks since a couple of cops were murdered. They have a pretty good idea of who did it, so why haven't these two suspects been brought in yet? The officers don't have any answers and file out to their vehicles, Jim with his two colleagues, to see if they can track any leads. The life of a law enforcer has been getting to Jim recently, and increasingly he is gaining a reputation as a violent and possibly out of control individual...
On Dangerous Ground was an RKO production from the time Howard Hughes had bought it and was running it into the (dangerous?) ground himself, which meant endless tinkering with productions which were taking ages to reach the screen, this being one of them. The most obvious example of that interference was the ending, which looked what it was, a tacked on conclusion from someone who did not have faith in material not only strong enough to bear a more melancholy denouement, but would have been strengthened by it. Before that, this was sturdy enough to be fairly impressive.
That's not to say there were no problems at all, for any thriller yarn which featured an angelic blind lady was always going to seem artificial, though there was a more melodramatic cant to the proceedings which made it tolerable in context. But the movie was almost halfway over before we reached that point, for the first forty minutes, near enough, had Ryan as that cop driven to the edge by the scum he has to deal with every day which has given him a very bleak view of human nature, so much so that Ida Lupino as said blind angel is filled with enough sweetness and light to have us accept that she could turn his life around and prevent the crash he is heading for.
During that long opening act, Wilson was a protagonist very typical of a Nicholas Ray film, which was just as well because that's what he was. With his usual mixture of tough guy attitude shot through with a curious vulnerability, Ryan was ideal for interpreting this director, and he convinces us that his character is giving into violence since his defences have been under attack by the depravity he has to deal with every day. In fact, it's only a matter of time before he kills somebody. After brutally roughing up one suspect, Wilson finds himself on an assignment out of town, his boss recognising the unstable cop needs a break before he's broken.
But the chief couldn't have reckoned with Mary Malden (Lupino also helping out on direction), an outpost of decency that Wilson didn't believe existed anymore - if only there weren't strings attached. The major string, more of a rope, really, is that her brother Danny (Sumner Williams) who she looks after since their mother has died is even more unstable than Wilson is, so much so that he has committed a sex murder on a young girl and the community are gunning for him, searching the countryside so they can lynch him, led by the victim's insane with grief father (Ward Bond). There's no hope for Danny, he did the crime, but Mary cannot bear to see him murdered when she believes he would be better served in a hospital and persuades the bemused Wilson to help out. Obviously there's only so far a Hollywood movie will go for redemption, so that quality is shifted to the hero, making for an admittedly contrived but compelling work. Bernard Herrmann's score helped, and the theme of finding good reasons not to give up and join the worst examples of humanity endured.