The crime busting character Jimmie Dale is back in yet another installment of the detective mystery novels. A wealthy playboy by day, at night he puts on inconspicuous dark clothes, a mask and a black slouch hat and becomes The Grey Seal, who enters businesses or homes and cracks safes, always leaving a diamond shaped, grey paper "seal" behind to mark his conquest but never taking anything. In this installment, he is hot on the trail of jewel thief Tom Braemer and the valuable necklace he is accused of having stolen. And the trail leads to Spike Dorlan, the notorious gangster, an encounter with whom can only portend doom for Dale and his companions…