When ARP warden Molly sees a light shining through the darkness of London on a cold winter's night in the middle of the blitz she's infuriated with the careless American who struck it. Doesn't he know there's a war on?
Guy's just trying to find his way through a maze of unlit streets. He's very sorry and Molly reluctantly forgives him. When he accompanies her on her nightly rounds the two learn about each other, themselves and whether it's really possible to fall in love in only one night - especially when there's no guarantee of tomorrow.