Seeing is Believing (also published as Cross of Murder) is a mystery novel by the American writer John Dickson Carr, who published it under the name of Carter Dickson.

It is a whodunnit and features the series detective Sir Henry Merrivale and his associate, Scotland Yard's Chief Inspector Humphrey Masters.

Arthur Fane arranges an unusual entertainment for his uncle, a long-term guest, and a few other witnesses—he hires Dr. Rich to hypnotise his wife Victoria.

The hypnotised Victoria is invited to shoot her husband, and refuses; when told to stab him, though, she agrees.

Although Sir Henry Merrivale is busily engaged in dictating his scandalous and slanderous memoirs to a ghost writer, he takes a hand to solve the murder with his friend Chief Inspector Masters, and brings things to a head just as another death occurs.