Two former naval officers who have served through the war return home and become entangled in a daring submarine salvage adventure to recover sunken wartime treasure. They join an undersea expedition that locates wrecks and hostile vessels, confronts spies and pirates, and faces technical perils including diving-bell entrapment and an impending explosion. A faithful canine companion aids their survival during desperate moments while improvised diving technology and a specialized submarine play central roles. Through courage, ingenuity, and teamwork they overcome adversaries, secure recovered riches, receive recognition, and at last return to their hometown.