East London, August 27 1939. Bob and Nan make plans for their wedding, and for their new flat; they are moving in a fortnight. Meanwhile, Tommy brings his new greyhound to his ma's Fish and Chip shop, claiming it is a pet.

3 September. War has been declared, and Bob and Nan decide to postpone the wedding. Bob runs into Tommy and his dog in the Hopvine pub, where the landlady has a son, Ted, in the Fire Brigade, Bob has lost his job, and he and Tommy decide to try their luck in the Auxiliary Fire Service. In the queue they meet petty criminal Sam, who is trying to evade a policeman, O'Brien. Ted shows them all to their dorm in an abandoned girls school. Another recruit, Brookes, tells of his time in Madrid with the International Brigade. One night, down at the docks, Sam and his accomplice spirit away a stolen barrel of Guinness.

As the AFS crew enjoy their Christmas party, they are called out. Tommy's dog, Short Head, who is due to race on Saturday, gives chase. But the call is a false alarm.

Ted and the AFS crew are called to serve at the main station, where the new boys undergo intensive training. Bob and Nan decide to go ahead with the wedding, and Bob's colleagues help him do up the new flat. When Short Head loses her race, Tommy finds himself unpopular with the others, who have all backed her.

The crew gets a callout, and Bob gets his first go on the ladder. Nan, worried, comes to the scene, and Bob promises that he will always call the phone box outside their flat when he's finished a job to let her know he's fine.

August 1940. O'Brien, is tailing Sam; Nan is expecting; Short Head is still losing. When Ted's girlfriend, Sue, gets short shrift from his disapproving ma, she goes dancing with Tommy instead. In the Hopvine, a drunken soldier taunts the AFS boys for their inactivity.

But one night German planes get through, and the AFS are called out. While Bob is on the ladder, he spots a telephone and decides to ring Nan. She promises she'll go to the shelter, but as she she's speaking she hears a bomb and runs from the phonebox just before it's destroyed, leaving Bob worried she's been killed.

Tommy, having a surreptitious cigarette, strays near an unexploded bomb; Ted blasts him out of the way with the hose, just before the bomb explodes.

Next morning. The all-clear sounds, and Nan leaves the shelter looking for Bob, who is still on duty. That night, the fire rages on. A bomb takes out the water main, and wrecks the Hopvine. Anxious, Ted asks Sue to try and find his parents.

Sue leads a team of wardens to the wrecked Hopvine; Ted's ma's abandoned handbag suggests she's nearby, and they eventually dig her and her husband from the collapsed cellar; Sue finally wins ma's respect. Meanwhile, Bob and Ted go on a hunt for petrol, and Bob goes looking for Nan.

The German planes come over for a third night, and the crew are moved to a new fire: in the warehouses opposite Bob's new flat. Bob takes a vantage point from the flat, but his orders are to save the warehouses; his own block will have to go. One consolation: he discovers Nan is ok; she's been taken to St John's hospital.

O'Brien tracks down Sam; he's caught Sam's accomplice, and now it's his turn. But another bomb explodes, pitching O'Brien into the river. Sam pulls him out, winning a temporary reprieve.

News arrives that St John's has been hit, and part of the crew is despatched to deal with the fire. When a bomb destroys part of one wing, Tommy runs up a ladder to help Chief McFarlane, who's trapped under a beam. But the floor collapses, leaving them both on a ledge. Shortly after, the roof caves in, killing them both.

Some time later. Bob and Nan's child is born, and they christen him Tommy. Tommy's ma attends the ceremony, grieving but proud.