Ella is ten, and loves inventing new things. Leo is three, and loves playing with his big sister. But sometimes Ella gets mad at Leo, especially when he keeps getting in the way of Ella's inventions. And when Ella invents a time machine, Leo is accidentally transported back to the age of the dinosaurs. Ella manages to save him, but Leo brings a dinosaur egg back to the present with him. The egg hatches, and Ella must find a way to save not only Leo, but the whole world.