Gambler Joe Garland is killed by an unknown assailant who passes u a fortune in jewels to steal an ordinary piece of flagstone. Caroline Jones gets help from Blackie through her fiancé Jack Evans and shows Blackie a letter from her blind father explaining the pieces of flagstone that are to be used by his three children as means of identification at the apportioning of his fortune. It is obvious to Blackie that the murderer is the third child but no one knows who he is.