Blackout — Robert Swindells

Life in a small village is boring now that the war is over, but when a group of children hear of some treasure kept locked in the village, things start to look a bit more interesting

It's September 1939, and Britain has just entered World War II, but in the small town of Golfodd there are no bombs, no soldiers, and no machine guns. For Tom, Mary, Gary, and Dil, the whole thing is a disappointment. They want excitement, but they aren't looking for trouble, so when they start shadowing the mysterious new woman in town, they don't expect it to lead them down to the bottom of the old, rotten mines of Golfodd. That's when things get dark and dangerous.