Through the Portal (Book One in the Through the Portal Trilogy)
by Justin Dennis
What's the worst part of falling through a portal to another world and not being able to get back? When the first person you meet almost gets you killed by a ferocious, fire-breathing dragon. Now, Jem, Oliver, and Sierra must set out across this new world to defeat the evil Veroci Regime that is stealing all the magic, but can they do it before the Dragon catches up with them?