It's good to see Chester Morris as this likable thief-turned-detective again; this is among his stronger roles. He’s trying hard to live an honest life, but finds himself caught up in a dangerous situation involving spying while he’s at Coney Island. His efforts to avoid the persistent "Insp. Farraday" (Richard Lane) are made more difficult by the fact that “Blackie” seems to be connected to every death that occurs! Things get even trickier when he unexpectedly encounters Rochelle Hudson ("Cecelia"), and ends up convincing her to help him, essentially becoming an accomplice. The mystery itself is fairly intricate; a deceased woman provides him with puzzling clues, and he must carefully assemble them to figure out who committed the crimes and clear his name. Knowing Morse code would be useful here – it’s much more effective than using signal flags in low light!

Source on TMDB