During World War II, a determined Canadian naval officer, Lieutenant Commander MacClain, sets out to exact revenge against the U-boats that destroyed his ship and crew. With the help of his new crew on the HMCS Donnacona, he embarks on a perilous journey across the Atlantic, battling against enemy submarines and Luftwaffe bombers in a desperate bid for survival and honor. As he faces down his nemesis, MacClain must also confront his own personal demons and the loss of his former comrades.