Ten-year-old Tula lives in a cottage at the edge of a Scottish forest. One day she discovers a small troll called Huva, his foot stuck under a tree root. Against his will she sets him free. According to troll law, he will now have to be her servant for the rest of his life-unless he saves her life in return. Huva cannot go home anyway;the Troll Court has taken away the key to his homeland to punish him for not being a wicked troll. The key has been hidden in another century. Huva would have to go down the Century Ladder to retrieve it. Only the naughtiest of trolls would dare to do that....