Zosia and James Amstad are nearly twins, born only eight months apart. Sixth graders, they desperately miss their father, a scientist who disappeared years before after experimenting with a method of transferring to other worlds and dimensions. Their teacher, Mrs. Grundle, torments them with glee, and stuffy Mr. Chauncey bores them to tears. But when they spot a troll near the tennis courts where their mother works as an instructor, and then find one of their balls has been replaced with a strange, fuzzy egg, their lives begin to get all too interesting and dangerous. Who is the dwarf troll? And what is inside the fuzzy egg? They consult Grandma Hecht, formerly a witch but out of practice, and she warns of curses. Then the egg hatches at school, and the ensuing chaos and attacks by dwarf trolls result in serious injury to their mother, enchanted and near death. With their heroic dog Nigel, they set out to find a cure for their mother and rescue their father, lost on a strange world parallel to their own.