12 year old Matt Dawson is annoyed at his parents and his foster sister, Rachel. Rachel tags along after Matt everywhere he goes, and it's pretty annoying. Before WWII, Matt's family lived in Minnesota. Now, they live in Canterbury, England so Matt's father could help with the war effort. Now that the war has started, Matt's older brother, Eric, has enlisted in the US Marines. But despite all of his griefs, he has one true friend, a retired firefighting German Shepherd named Chief.
Matt and his family know what to do in case of an air raid, even though there hasn't been one yet. On June 1, 1942, in the middle of the night, they hear the air raid sirens. Matt's dad is still at work and his mom needs to help their neighbor get to the shelter under the cathedral. Matt, Rachel and Chief get to the shelter safely, but they start to worry when they're parents don't show up. After a while, his parents come in, but his dad has some bad news, Eric is MIA (Missing in Action).
Hearing this news, he runs out of the shelter into the street just as bombs and incendiaries are dropping. When Chief comes out looking for him, a bomb explodes nearby, and both Matt and Chief are separated and confused. When Matt gets up, he heads upstairs, ending up on the cathedral roof. There, he finds firewatchers throwing bombs off the building to prevent a fire. When he turns around, he finds, unsurprisingly, that Rachel followed him. When she catches her breath, Rachel tells Matt that she saw Chief roaming about in the city.
When Matt and Rachel head back downstairs to look for Chief, they see a parachute falling from the sky. When they reach where the parachute landed, Matt tries to help the soldier out of the river. The soldier tells them that he is Scottish, but he starts talking in German. Rachel realizes it and tells Matt to let go. The German soldier tells the kids that he will turn himself in if they save his life. So, Matt and Rachel help him up, not knowing that he was lying. The German takes Matt by the arm and is about to stab him with a knife, when Rachel pummels the soldier in the head with a branch. For the next couple of hours, they are running from this soldier.
Meanwhile, Chief is having his own troubles. He is still lost, but when he runs into a burning building to save an injured man, he comes out finding himself in the care of an American soldier named Landry. Landry takes one look at how Chief reacts to danger, and he thinks that Chief is a natural search and rescue dog. So, Landry and Chief walk throughout Canterbury, searching for survivors through the flames, dust, and rubble left behind by the bombs.
Can Matt, Rachel, their parents and Chief be reunited as one, big, happy family?