Against the background of WWII, Tuur’s friendship with Lambert is tested when both boys befriend new girl Maartje. The secret she holds will put all three of their lives in danger.

It’s 1943, but for friends Tuur and Lambert (12), the German occupation is merely inspiration for their exciting cave-war games. Then the Jewish Maartje joins their class. Tuur distances himself from Lambert when he discovers his own father is a member of the resistance, while Lambert's father is a member of the Dutch fascist party. Maartje is arrested after Lambert tells his father about her hidden pig. Lambert makes up for his betrayal by helping Tuur and his family escape to Belgium.