The Vriends family has adopted Dolfje and treated him as one of their own, especially 'own' firstborn son Timmie is the perfect devoted big brother. At his seventh birthday, Dolfje's spectacularly different DNA kicks in : full moon causes him to turn werewolf three consecutive nights. The school's Christmas play Peter and the Wold helps the brothers cover up, but they can't resist putting class bully Nico Pochmans in his place and raiding the busybody neighbor's chicken den doesn't exactly help. She alerts a grim anti-alien society, while Dolfje feels akin to a mysterious lurker in the know, whose own secret proves intertwined. As the parents find out, especially the pleasantly-weird father remains unconditionally supportive.