By night, wealthy clubman Jimmie Dale becomes the Gray Seal, a master criminal who uses his skills for justice. But after years of retirement, he's drawn back into his dangerous double life when his fiancée Marie sends an urgent message: their mutual friend Ray Thorne is in deadly danger. A mysterious blue envelope has arrived at Ray's home, making him the target of a ruthless criminal gang led by the notorious Daddy Ratzler. When Jimmie breaks into Ray's safe to steal the envelope and protect him, tragedy strikes—Ray is murdered, and the Gray Seal is blamed for the crime. Now Jimmie must navigate the shadowy underworld he thought he'd left behind, donning disguises and risking everything to clear his name and find the real killer. From elegant gentleman's clubs to squalid dives, from New York's dangerous back alleys to isolated country estates, Jimmie pursues the truth about the blue envelope's contents and the identity of Ray's murderer. With police hunting him and criminals plotting his demise, can Jimmie Dale solve the mystery before he becomes the next victim?