S03E25: The Case of the Irate Inventor

James Frazer wants a divorce and his cheating wife refuses to give him one. She's also stealing the plans to his invention in order to bait her engineer lover into staying around. Frazer leaves town for three months in order to cool down, but on the night of his return he finds his wife murdered in his office—and he has the only key to a unique, burglar-proof lock that he invented.