Second in the Dragon Knights series, which is a different take on dragonriders; it resembles Anne McCaffrey's Pern books but is definitely for adult readers. The story starts with Lord Darian of Skithdron bedding a woman in a palace in order to gain access to secrets. He then decides that Lord Venerai and his ruler King Lucan are both deranged and evil.
Two neighouring kingdoms, Draconia and Skithdron, are at odds and while the former boasts dragons as native beings, the latter has venomous serpentine beasts called skiths. These usually solitary creatures are being controlled for use in warfare by King Lucan. Adora, a healer woman, has just been seriously wounded by skiths and saved by a dragon, and now she is resting in the BORDER LAIR while her injuries heal. An older dragon knight called Jared, bonded to a female dragon called Kelzy, is caring for her and gradually falling for the courageous woman. Prince Nico of Draconia arrives and discerns that Adora is likely to be of lost royal blood, as she can 'hear' dragon speech and magically heal others.
Belora, daughter of Adora, is also working as a healer, and mated to two dragon knights - women being scarce, the men willingly share a partner. Warfare is now waged openly between the kingdoms, the dragons flaming the skiths, which spit back acidic venom, while diamond-tipped crossbow bolts capable of piercing dragon scales are suddenly brought into use by the Skithdrons. Darius, fearing that the evil magic he has witnessed is taking over King Lucan, decides to defect in order to warn Draconia, thereby putting himself into grave peril. Meanwhile Adora is the subject of a well-meaning conspiracy by the dragon Kelzy, who decides that the woman requires two dragon knight mates.
This is part of a complex series but can be read as a standalone, with sympathetic characters and well-imagined medieval warfare. Be warned, it features threesomes in a loving relationship between three life partners. Bianca D'Arc has written several books in this and her other fantasy series. I enjoyed this exciting tale and will be looking out for more of her work.