A seven-man lightship crew prepare themselves for their relief crew to arrive. Spirits are high as they look forward to returning home, where one of the younger crew is due to get married. A mine drifts dangerously close. Below deck, the crew have fun hiding old Lofty's pet tortoise and fixing it to be his turn to empty the slops; on doing so he spots the mine. Using the dinghy, they tow the mine out of reach and a minesweeper, responding to their distress signal, arrives and destroys it. The crew sing as they continue with homeward preparations. On deck. Lofty explains how, in the last war, the German pilots would wave as they flew over. Relaxed, they watch two German bombers approach and are surprised to come under machine gun fire. The captain is wounded in the arm. Unaware of the attack, command redirects the relief ship, ordering it to carry out emergency repairs on another lightship. The Nazi planes start dropping bombs as the crew take to the lifeboat and, leaving Lofty's tortoise, they watch the lightship go down.

Night falls and both a merchant and a military vessel, experiencing navigational problems without the lightship, have to anchor. The shipwrecked lightship crew row on through the night, becoming delirious and weary. At dawn they see the shore but they are too tired to land the boat and all seven are killed in the cold sea as the dinghy capsizes in the surf.