On the night before he sails in search of the steamship Arcadia's sunken gold, Paul Sinclair (Bruce Bennett)meets Madeliene Nielson (Anita Louise) in a San Francisco nightclub. On the second day at sea, Madeliene turns up as a stowaway. While diving and searching for the sunken gold, off the Phillipines, Paul discovers that a foreign-country submarine has been laying mines in order to completely cut off the Phillipines from American protection.

"UNMASKING A NEW THREAT TO AMERICA'S DEFENSE!"