The Door in Lake Mallion: The Brindlewatch Quintet, Book Two - S.M. Beiko

The Door in Lake Mallion brings readers into a world of magic, monsters, and the folks who love them, telling a story of dazzling performers, glowing mushroom cities, and the power of shining our light for everyone to see
Dunstan has had big ambitions his entire life — bigger than the small lakeside town of Knockum — imagining himself heading a chorus line with a leading man he hasn't quite cast yet. But on his way out of town for good, a gang of his classmates capture him and send him to the bottom of nearby Lake Mallion, rumored to harbor a magical door in its depths.
Before Dunstan drowns, the door opens. On the other side is the Geodom of Jet and the reptilian Prince Ven, who is on the run — from his past, his destiny, and the stories people tell about him. Now Ven has a chance to tell a different story, and he'll use Dunstan to pen the script.
But the door has been keeping a dangerous secret that not even the lakebed can contain, and both worlds hang in the balance. Will the final curtain reveal that not all lights are meant to shine?