Trickster by Christina Bauer

Aldred, the dreaded Earl of Acca, is at it again. After discovering a new kind of fighting arbor, Aldred rips open a gateway to another world called the Primeval. The earl’s goal? Release the arbor, lock in an easy kill, and show off some supposed prowess as a slayer of unusual big bads.

After all, how hard can it be to kill a freaking tree? Super hard, as it turns out.

The earl unleashes none other than the Contagion, an uber-evil wizard in tree form. What happens next is nothing less than a disaster. The Contagion races through the portal, steals the life force of local children, and then escapes back into the Primeval. No one wants to chase after the cruel wizard, even if destroying the Contagion means healing the injured innocents.

Cue our hero, Lincoln, and his fiancée, Myla.

While everyone else runs away, Myla and Lincoln break into the Primeval with a single goal: hunt down the Contagion. Unfortunately, the couple’s only guide to the strange realm is Peli, a trickster monkey who may be in the Contagion’s service. And that isn’t the only possible treachery that Myla and Lincoln face, either. Powerful forces could be deceiving our favorite couple about the very nature of who they are and what they want.

Talk about tricksy.