Hero's continued lack of success in anti-submarine warfare exercises against HM Submarine Ovid rattle Captain Glenn's self-confidence and cause increasing tension between him and his officers. Ovid's captain and Glenn's old friend, Commander Tremayne, offers to set up a new exercise and make it into more of a learning experience for Glenn, but the constant changes in the training program and Glenn's apparent lack of concern for his crew lead to a showdown between him and his first lieutenant, Lt. Commander Beaumont.