An ordinary raincoat finds its way to the Black Museum, and we learn about the crime that put it there. Robbers in white cloth masks took no jewelry, and the only victim was the young man shopping for a wedding ring. How will the anonymous, shabby raincoat link the robbers to the scene? The pistol used in the crime is in the pocket, but it was a stolen one. A glimmer of hope comes when the coat was traced to certain possible shops, and the tedious police work begins.
A suspect is identified. Through interrogation, and more police footwork, others are tracked down. Do the cops have their killer? Which of the bandits did the deed? Does it matter? With no honor among thieves, a confession of matters is presented dramatically as drunken bandits throw together their hasty plan to do the robbery job.
The pieces of the puzzle fall quickly into the laps of the cops. The outcome of the trial is summarized as each bandit got what they deserved.