When America enters World War I, German-American Oscar Krug is thought to be an enemy sympathizer due to his name. He fights his foes to prove that they are wrong, then immediately enlists and is assigned to the merchant marines. The night before boarding, he marries his sweetheart, Alice Morse, and she sails with him, disguised as a Red Cross nurse. A German submarine torpedoes the craft and sinks it. Krug and his bride board a lifeboat, where the sub finds them a couple of days later. The Germans take Alice and leave Krug, who swears revenge to the commander. Krug is saved by a passing ship and gets his chance a year later when he is in charge of another ship. It blows up a sub, and Krug sees the commander — the same man he is looking for — in the water. He pulls the commander on board and tricks him into telling Krug the details of how the commander ravished Alice and threw her body overboard. Then Krug reveals his identity and skins him alive.