Space Lizards Ate My Sister! — Mark Griffiths

Asteroid Peach is heading straight for Earth, and the planet will be destroyed in a matter of days. In desperation the world turns to the evil space lizard Admiral Skink, currently imprisoned in Cottelton police station in the body of Pickles the iguana. In return for his freedom, Admiral Skink promises to destroy the asteroid and save Earth, but instead he builds a wormhole bridge to his home planet, Swerdlix, and escapes! And just as Skink is making his getaway, a giant thrall-beast emerges from the wormhole, promptly eating Sally Spratley, Lance's little sister.

It's up to Lance and his best friend, Tori, to travel to Swerdlix, capture Admiral Skink, stop the asteroid from destroying humanity, and find some flooblescoop powder to make the thrall-beast sneeze out Sally ... which shouldn't be that hard, should it?