You cannot have a murder without motive. The first crime was different—there we had a rich lover waiting to step into her husband’s shoes.” “Money is not the only motive for murder,” I objected. “True,” agreed Poirot placidly. “There are two others, the crime passionnel is one. And there is the third rare motive, murder for an idea, which implies some form of mental derangement on the part of the murderer. Homicidal mania and religious fanaticism belong to that class. We can rule it out here.”
