While staying with his weird great-aunt Kathryn, Evan visits a funky old toy store and buys a dusty can of monster blood. It's fun to play with at first. And Evan's dog, Trigger, likes it so much, he eats some! But then Evan notices something weird about the green, slimy stuff-it seems to be growing. And growing. And growing. And all that growing has given the monster blood a monstrous appetite...

Evan is flying to Atlanta to meet his parents, as the family is moving due to his father's job. On the plane, Evan meets three kids. But as each of them get to know Evan more, Evan tells them about the monster blood. And all the trouble it caused. However, none of them believe him. Though, that's going to change soon. Very soon. Because the monster blood has followed Evan. And now it's going to cause a very frightening flight...