"The Problem of Thor Bridge" is a Sherlock Holmes murder mystery by Arthur Conan Doyle in The Case-Book of Sherlock Holmes, first published in 1922 in The Strand Magazine.
Neil Gibson, the Gold King and former Senator from "some Western state", approaches Holmes to investigate the murder of his wife Maria in order to clear his children's governess, Grace Dunbar, of the crime. It soon emerges that Mr. Gibson's marriage had been unhappy and he treated his wife very badly. He had fallen in love with her when he met her in Brazil, but soon realised they had nothing in common. He became attracted to Miss Dunbar; since he could not marry her, he had attempted to please her in other ways, such as trying to help people less fortunate than himself.