A young man, Guy Wallingford, bursts into March's office and exclaims "They've stolen the monkey." Guy explains that he he had already talked to Inspector Ames and that Ames told him to go to March saying that March "handled the monkey business end of the profession." Guy is a brilliant but mentally unstable scientist who works at the lab of the eminent scientist, Sir George Watkins. Guy and two other researchers are doing cancer research using monkeys to test their theories. Guy insists one of the test monkeys has been substituted. Guy becomes increasingly distraught and when he later is found dead from gas, Ames readily believes it to have been suicide. There is a very clever solution to the mystery which March in his usual urbane manner sorts out. However, I believe even medical research experiments using animals is just plain wrong and so this episode was distasteful to me.