Dr. Charles Reese and his assistant Ann Patten have invented an odourless cleaning fluid which has tremendous commerial potentialities. Reese's wife, however, is a scheming and vindictive woman who is jealous of their professional proximity and she refuses to allow the invention to be sold. Charles and Ann are actually in love and Mrs. Reese has had their perfectly innocent movements traced by a private detective. When she is found murdered, the cause of death being poisoning by one of the chemicals prevalent in the cleaning fluid, a number of suspects are questioned by the police, including Charles, Ann, Schofield the family solicitor, the daily woman Mrs. Turbey, and Mr. Senior the rather unwhoesome detective, who, it is discovered, had been Mrs. Reese's lover. Charles is arrested - the case against him is very strong, but Ann, positive he is innocent, discovers clues which point to Senior's having committed the murder. She discloses them to Mr. Schofield, who appears to believe her. But Schofield has absolute proof that Senior was elsewhere at the time of the murder, and he soon sees how Ann sympathizing with her desperate attempt to free the man she loves, he cannot condone her incrimination of the futile and pathetic detective, and he arranges for the police to overhear the confession he extracts from her.