A New Yorker hobo moves into a mansion and along the way he gathers friends to live in the house with him. Before he knows it, he is living with the actual home owners.

For Miranda Wells, moving to New York to live in Dragonwyck Manor with her rich cousin, Nicholas, seems like a dream. However, the situation gradually becomes nightmarish. She observes Nicholas' troubled relationship with his tenant farmers, as well as with his daughter, to whom Miranda serves as governess. Her relationship with Nicholas intensifies after his wife dies, but his mental imbalance threatens any hope of happiness.

Merchant Marine sailors Joe Rossi (Humphrey Bogart) and Steve Jarvis (Raymond Massey) are charged with getting a supply vessel to Russian allies as part of a sea convoy. When the group of ships comes under attack from a German U-boat, Rossi and Jarvis navigate through dangerous waters to evade Nazi naval forces. Though their mission across the Atlantic is extremely treacherous, they are motivated by the opportunity to strike back at the Germans, who sank one of their earlier ships.