After Midnight with Boston Blackie

Ed Barnaby is paroled and determined to give the diamonds to his daughter. He hides the jewels in a safe deposit box at the Arcade Building. Knowing that shady characters are after the diamonds, he keeps a low profile to stay ahead of them.

Betty receives a call asking her to meet him at the Arcade Building, but Barnaby never arrives. She contacts Boston Blackie for help, sensing danger and the looming treasure. Blackie agrees to assist and starts coordinating a plan.

Blackie delivers Betty to Arthur Manleder's apartment for safekeeping and warns that Barnaby's enemies won't pause. He ensures her protection while the danger closes in. The Runt's engagement to Dixy Rose Blossom is postponed due to these events.

Blackie identifies the exact deposit box Barnaby used and plans to recover the diamonds. Meanwhile, the crooks torture Barnaby to reveal the hiding place, and he manages one last plea by calling the police before Herschel kills him. The deadly confrontation underscores the danger surrounding the jewels.

Inspector Farraday and Sergeant Mathews rush to the Arcade Building as Blackie is about to open the box, hoping to arrest him for Barnaby's murder. They discover the box is empty and Blackie escapes custody. The search for the missing diamonds intensifies.

Betty is kidnapped from Manleder's apartment, and a note demands the diamonds in exchange for her freedom. Blackie has the Runt borrow a Dixy brooch to help test whether the stones are real by prying off fake ones. The plan heightens the stakes as the clock ticks.

Blackie goes to the Flamingo Club, run by Herschel and associates. He slips inside and watches through the keyhole as the crooks stash the diamonds in a safe. The tension of the caper tightens as the heist unfolds.

Blackie cracks the safe and pockets the jewels, but Walsh and Beck burst in before he can leave. He escapes with the jewels still at stake, triggering a tense pursuit. He then changes strategy to keep the diamonds from falling into the wrong hands.

Walsh and Beck exchange Betty for the fake diamonds, unaware that Herschel has the real ones. Herschel returns too soon and the fakes are exposed, but Blackie and Betty manage to escape aided by a citywide wartime blackout. The blackout helps them slip away amid the chaos.

Walsh realizes Herschel is acting for himself and cannot produce the diamonds. He shoots Herschel, and Blackie witnesses the murder. The balance of power shifts as Blackie stakes a claim on the diamonds.

Blackie offers to give the jewels to Walsh in exchange for the location of Barnaby's body. The police close in, forcing Blackie and Walsh to flee and steal Inspector Farraday's car. The stakes rise as the chase approaches a climax.

Blackie rigs the car radio to transmit Walsh's confession to the police listening in. He coaxes Walsh into talking, then turns the tables and hands him over to the authorities. The plan squeezes the criminals into custody.

The Runt's wedding to Dixy Rose Blossom is interrupted again, as Farraday and Mathews arrest Dixy for bigamy. The arrest marks a chaotic wrap to the diamond caper, with justice bending the rules to corner the final criminals. Blackie and Betty end the case with a narrow escape amid the fallout.