Summary from inside flap of book jacket:
"It is the fall of 1944, and Worl War II grinds on. Although the Germans have occupied Holland, the courageous Resistance movement constantly undermines them. Thirteen-year-old Pieter Van Dirk, who is part of the Resistance, knows there's a traitor in his village--someone who would reveal his identity to the Nazis if his undercover work is discovered. But who is it?
As Pieter takes more and more chances, the shadow of the traitor is everywhere. The obvious suspects are the Nazi soldiers, but Pieter begins to wonder if it's one of the villagers themselves. Could it be Mr. Van Der Meer, who teaches his students about German writers? The local doctor, who treats German soldiers? His uncle, who feeds them at his tavern? The suspects multiply as the suspense increases--and the stakes grow higher.
Rich in historical detail and inspired by real people and actual events, this story shows us the many faces of World War II."
I read this a few years ago, when I was 13, and I really enjoyed it. As the book went on, it got more and more suspenseful, until it finally came to the climax near the end. I think that the summary about sums it up!