Herrick and Slocum find a message in a bottle that alleges a ship thought to have been lost at sea due to a fire was scuttled to cover up illegal munitions trading. Instead of turning the note over to the authorities, Herrick launches his own investigation placing him and his friends in deadly peril.
Captain John finds himself drawn into the hostilities between Danny Cook, a young man he once mentored, and Darryl Benson, a Korean war vet and Cook's rival for the affections of pretty Madge O'Hara. Jealousy leads to a murder plot on a bridge trestle, but Captain John could become the unintended victim.
Captain Ed Conway, an old friend of Captain Herrick's, buys an equally ancient tugboat hoping it will be the foundation of his own company. Conway is mystified when flashy George Mallory offers to buy his old tub for more money than it's worth and then concerned when he finds his ship sabotaged after turning down Mallory's offer.