Crown and Dragon by Alisha Klapheke

The grumpy/sunshine, dragon-riding duo is back…
What do tomatoes, scowling, and artifacts that could end the entire world have in common?
You guessed it—Tahlia and Marius.
When the Fae king sends dragon riders Tahlia and Marius on an undercover mission to recover the invisible crown, an artifact that gives the wearer the ability to control minds—and a host of other nasty things—it’s clear there will be danger.
For one thing, the madman currently in possession of the crown has a bit of a god complex. But danger is nothing new. And the mission will finally allow Tahlia a chance to cross the Veil and explore the world of humans, not to mention making Marius wear a ridiculous costume, which is pretty much Tahlia’s favorite part of the whole thing.
Tahlia is fairly certain they’ll win the day. But when they discover the crown is hidden behind a labyrinth of deadly traps, her hope withers. If they don’t succeed, her soul-bonded dragon will never fly again. She might even die.
So yeah, failure isn’t an option.