Cynthia Blair, the fourth owner of China Bank, opens her home in a tangible expression of thanks and support to members of the Pacific Submarine Fleet Force for their extraordinary service to the United States. When former shipmates reunite at Blair Mansion, they unwittingly become involved in the most brazen hijacking attempt the U.S. Navy has ever seen. Lieutenant Commander Charley Jason and Polly Flowers' wedding is set to occur at the mansion the night before inspections will be held on the "Piratefish" and "Minefish" submarines. Also coinciding with the wedding festivities is a secret mission designed by Colonel Mark Hong, a Red Chinese officer and agent extraordinaire. Disguised as a bank interne, Hong arrives at Blair Mansion for his training in American banking. After members of his gang clandestinely slip ashore, they immediately begin terrorizing the residents of Chinatown and proceed step-by-step toward their target. Late on the night of the wedding, the gang takes hostages and seizes control of a submarine at Treasure Island. Chief Gunnersmate Carruther and Lieutenant Sylvester of the "Piratefish" interrupt the hijacking with their own counterattack. Will Carruther and Sylvester be able to save the hostages and the submarine in the midst of the explosive action in the waters off the Golden Gate?