 In 1943,  Mac  MacClain, Canadian Navy, has lost his ship and many men to a German torpedo. While waiting for a new ship, he befriends Joyce Cartwright, sister of one of his dead officers. We follow the building and launch of new Corvette K-255, the  HMCS Donnacona . And who should be Mac s new subaltern but Joyce s other brother Paul, fresh out of the academy. Mac will do his best to make a good officer of Paul...if they both survive their hazardous sea duty.