Major James Kelly leads a team of three ex-convicts into Confederate territory to destroy a submarine under construction in Mobile, Alabama. Kelly, posturing as a medical device salesman, gains access to the Naval Hospital and the dockyard in Mobile. Follow the team's intelligence gathering and execution of a night time raid. Upon completion of the mission in Mobile, Kelly and his men are ordered to San Francisco via the Panama Railroad. In California, they foil a plot to install a pro-slavery State Government. Kelly's last years are spent as the founder of a Pinkerton Security Agency in Boston, Massachusetts.