"The Problem of Thor Bridge" is a creative Sherlock Holmes adventure, demonstrating that even as Arthur Conan Doyle was drawing to the end of his stories about the character (not for the first time), he still had a few clever ideas kicking around.
Holmes is hired by a former U.S. Senator to investigate the murder of his wife. The evidence seems beyond doubt that the family governess arranged a clandestine nighttime meeting on a bridge for the purpose of murdering the woman. But the Senator steadfastly believes in the innocence of the governess, and wants Holmes to prove it. The twist in the tale comes with the manner in which the governess was framed, and the surprising party responsible.
"Thor Bridge," with its memorable death, has figured in several subsequent adaptations. The CBS series Elementary, for example, has alluded to it on two occasions. But it sticks in the mind for good reason; like a magician's trick, it turns on a surprisingly simple mechanism to mislead and confound the audience. Here, the perpetrator has a quite simple but potent way of disposing of the weapon, casting doubt on the entire crime scene. It's so tantalizing, you can overlook the possibly questionable motives of the perpetrator -- is death really the answer here? You can also overlook the question of whether a normal police investigation might not have recovered the weapon in due course. (Though the fact that the governess is being railroaded helps with this.)