At a party aboard his houseboat given by Mr. White, the district attorney, the lights are extinguished following the theft of a valuable diamond necklace to allow the guilty party to return it with no questions asked. When the lights are turned on, White is found murdered. Mr. Green, the coroner arrives to pronounce the victim dead, but is pressed into service to investigate the crime, which he is reluctant to do for fear of missing the show for which he has a pair of tickets. Green discovers Dorothy, the district attorney's ward, hidden in a grandfather's clock, clutching the missing necklace. She claims that she was handed the necklace and pushed into the clock while the lights were out. As Green prepares to take everyone's fingerprints, the lights are again turned off. The coroner is attacked by a figure, who is revealed to be the dead man's deaf and dumb valet. Green calls in a "jury" of working people to pass judgment on the evidence. As the valet assists in the recreation of the crime, he himself is murdered when the lights are again turned off. Green continues the effort to recreate the crime, taking the victim's role himself. Yet again, the lights are turned off, and yet again there is a body on the floor--but this time still alive and wrapped in a shawl. The new victim is reveled to be Mr. Black, the Deputy District Attorney. The coroner publicly accuses Dorothy, and asks Black to serve as State's witness against her, but by a ruse manages to obtain his fingerprint, revealing that Black is indeed the murderer. As news photographers come in to take his picture, Green proposes to Dorothy and they rush off to the theater to catch the show.