HMS Duncan and her crew face increasing pressure in the Strait of Hormuz as Iran steps up its efforts to capture a second British tanker. Three weeks into Duncan's mission, Iran is still holding the Stena Impero captive, but international pressure is mounting against them. The ship is ordered to hold the line and continue escorting fuel tankers safely through the Strait, while awaiting relief by HMS Kent. When a fire breaks out in the engine room, it threatens the ship and the lives of some of the crew.