For centuries, explorers have searched inside shipwrecks for gold, but there has never been a treasure trove as valuable - or as difficult to recover - as that lost in the waters of the Barents Sea in 1941. British light cruiser HMS Edinburgh was assigned the dangerous mission of escorting an Arctic convoy to the Soviet Union. But on her trip home, laden with Russian gold, the warship was attacked by a German U-boat. Edinburgh's fight for survival and the audacious operation launched to recover the gold decades later tell a remarkable forgotten story of bravery above and below the sea.