Before committing suicide, Harold Grant posts three letters - one to his wife, one to his business partner, and one to a third party. The first two letters are highly damaging to their recipients, who dare not show them to the police. But who has got the third letter, and what does it say? The recipients of the first two are sick with anxiety on this score. Thus begins a strange chain of events, out of which develop both a love affair and a bloody murder ...