A nurse in the Caribbean turns to voodoo in hopes of curing her patient, a mindless woman whose husband she's fallen in love with.

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.

Ambassador Joseph Davies is sent by FDR to Russia to learn about the Soviet system and returns to the US as an advocate of socialism.