Black Cats are Lucky — A.E. Fielding

When Sir Henry Bachelor was found dead in his library, a bottle of poison clutched in his hand, it would have been assumed to have been a suicide, except for two facts. One, was that his most recent will was missing. The other, is that the poison that killed him was not the same poison as that in the bottle. When this latter fact is discovered, Scotland Yard's Chief Inspector Pointer is called in to sort the case out, a task made more difficult by too many of those involved keeping too many secrets to themselves. The solution to the case, though, depends on the actions of a black cat named Luck .