Susan Cooper 
Dawn of Fear [EPUB ebook] 

Sirens are blaring. Families huddle in bomb shelters. A nearby city is in flames.For Derek and his friends, night-time air raids are a normal part of everyday life. When a particularly violent raid closes their school for a few days, the boys use the time to complete construction of their secret camp. But to their horror, their refuge is savagely attacked by a rival neighbourhood gang. And then, after one night filled with bombing, the war changes his world forever.