While brothers Lexington and Socrates Smith, authority on fingerprints and blood stains, are guests of Peter Mandle and his stepdaughter, they observe a light flashing from the direction of Mr Jethroe s house. COME THREE OAKS, it spells in Morse. A ghostly figure is seen hurrying across the moonlit lawn. Early next morning the brothers take a stroll and there, tied to an oak branch-is a body, a purple mark where the bullet struck.