Jack dreads summer because his single mother has to work and leaves him at home with his boring little sister who is autistic. She doesn't talk at all. Ever. But one day while they are at a flea market, she does talk. She tells Jack to trade their mother's car for a box of mysterious seeds. It's the best mistake Jack has ever made!

"Like a bolt from the blue, Jack's little sister Maddy is gone--carried into another realm by an ogre. When Jack and Lilly follow Maddy's captor through the portal, they are ready for anything . . . except what they find waiting for them in the floating crossroads between worlds. Even the power of their magic plants may not be enough to get them back to earth alive. Alone and injured, Jack and Lilly must each face their own monsters--as well as giants who grind the bones of human children to feed their "beast" and a fearsome goblin king in the sewers down below. But when Jack finds himself in a tough spot, help comes from the most unlikely person: the goblin king!" --page [4] of cover.

"Teaming up with new friend Zita the spacegirl, Jack and Lilly confront an army of dangerous giants and screeds ready to lay siege to Earth and determined to end all human life."--Provided by publisher.