Came Back Haunted - The Cambion Rider Chronicles, #3

Parleying with an ancient dragon comes with strings attached, and a ruthlessly grim psychological cost, that alters the lives of Veronica and Lachlan. A group of young dragons and riders enters the territory of an ancient dragon uninvited. It sounds like the set up to a fable decrying foolish behavior. Nevertheless, newly appointed chieftains of their dragon colony, Lachlan and his cambion-dragon rider, Veronica, are willing to take that risk, if it means Veronica will learn to harness and control her demonic abilities.  Upon their arrival into Swain's territory, the elder dragon makes them an offer: he will take Veronica under his wing, if the colony agrees to find Tarik.
The only son of Swain's favorite concubine. With the bargain is struck, the young colony becomes entangled in a web of deceit, secrets, and betrayal.  Soon, Veronica and Lachlan learn things are more duplicitous than they initially appeared, and the true cost of Swain's tutelage comes with a treacherous price tag.