 When his parents are too busy to take him to the park, a bratty boy named Gus, followed by his toddler sister Rosie, take off on their own. While Gus plays with his toy boat, Rosie gets herself into a large underground area. There she meets Stanley, a friendly troll with a green thumb that will grow a flower at his thumb s touch. This run-down underground cave is now Stanley s home after he is exiled to Central Park from his home world, a terrible loveless dark troll world, for growing flowers. Gus is introduced to Stanley by Rosie and is not impressed. But when Gnorga, the evil queen of the troll world, comes to Manhattan armed with her purple thumb that turns things to stone, she sniffs Stanley out, with intentions of bringing Stanley, his friends and the city to a terrible conclusion.