Well, that might have been a mistake. It turns out the papers contain a valuable secret formula recently acquired by enemy spies. The spies, naturally, want the formula back.
Jack stole the notebook from the lovely Nan Baker (June Kennedy), who actually isn't a spy herself. Her boyfriend is, though, and he was using her as an unwitting mule to bring the papers into the city. When she tells him about the theft, he tells her the papers contain sensitive business contracts for one of his clients. He puts her to work trying to track them down without involving the police.
This drops her into a sleazy world of sleazier informants and even the world's sleaziest pawnbroker. This eventually brings her to Jack, who tries to pawn a fake notebook off on her. Remember, he thinks the real thing went out with the trash. Actually, though, they ended up lining his landlady's cat box. The papers are now kind of smelly, but they are still valuable.
Jack, by now, has been beaten up by the spies and the pawn broker he worked with has been murdered. He has realized what the papers must be and tries to sell them back, using Nan as a go-between. But Nan is slowly realizing that her boyfriend is a fink and to also realize what the papers are. She wants to do the right thing. Jack wants to get some quick cash and not get killed.
Everything comes to a head in an abandoned warehouse, where Jack takes a bullet wound, but then suddenly finds himself in a position to do something heroic for the first time in his otherwise rotten life.
The movie has its flaws. Most notably, the initially cool-sounding jazz score gets repetitive over the movie's relatively short run time.
But I still like it and recommend it. It has some nice visual moments, especially while Jack is pulling off his burglary during the opening credits. The plot takes some fun twists and turns, while Hogan brings a sense of humanity to his role--Jack is mostly a rotten person, but he has a few flashes of conscience over the course of the story that give the decisions he makes at the climax some sincerity. This is helped by the fact that to a large degree, he's forced into the role of hero and might still have looked out only for himself if he'd been able to. Both we and Jack will always wonder what he would have done if he'd had more options.
Nan's boyfriend is another good character. He's using her, but there are hints that he might actually care for her--feelings that affect his actions in important ways when he too ends up in that warehouse.
It's a minor point, but I appreciate that the number of bullets fired from revolvers is kept to six apiece in the final confrontation and that this plays a role in the outcome.
I had originally posted a link to the movie on YouTube, but that has sadly vanished. If you have Amazon Prime, it is available there.