Doyle was the Captain of the Queen's Ravens, her assassin, and the acknowledged champion of the Unseelie Court. It was said that when he speaks the Queen's words come out. His livery is a spider. He is often referred to by Andais as "My Darkness" or in general, "The Queen's Darkness."
Doyle is capable of traveling through mirrors as well as communicating through them. He is able to shape shift into a Gabriel Ratchet (hellhound or hound of the hunt), a horse, and an eagle. He is able to bespell others with flickering lights in his eyes. Doyle is also known as the Bearer of the Painful Flame, a sickly greenish flame able to bring the true death to immortals.
Doyle had been the Queen's Darkness for over a thousand years, and though he loved her once, his loyalties have shifted to Meredith.
Doyle does not like modern modes of transportation such as airplanes or cars; there is too much metal in either mode of transport for him to ever feel truly comfortable.
In A Lick of Frost, it is revealed that he is one of the fathers of Merry's children and therefore will be a king to her queen.
Bainidhe Dub - Black Madness - A sword that brings madness upon any who might try to wield it other than Doyle.
Snick and Snack - Twin black daggers forged together at the time of their making. The daggers are able to hit any target once thrown. Their true names have been forgotten.
Doyle was sent by the Queen to Los Angeles to bring Meredith home. He saved Meredith from Alistair Norton by sending spiders through the wards around the house and warned Meredith to hide before he ultimately shattered the mirrors. He revealed later that he watched the ritual between Merry and Roane. His observation to Merry was that two sections of the bed's headboard were melted, indicating that Merry would later manifest two hands of power.
Doyle serveed as her protector again when Merry was being pursued by the sluagh and came through the mirror into the bathroom to rescue her. Once with her, Doyle revealed he was sent by the Queen and gave Merry the Queen's mark of protection through a kiss.
Doyle later revealed the meaning behind the nickname, Baron Sweet-Tongue when he healed Merry's wounds at her apartment. He then escorted her back to the Unseelie court, and while there, serveed as a constant support as she confronted her cousin Cel, awakened the roses, and set up alliances with the goblins.
It was in this book that Doyle's loyalty to the Queen began to waver toward Merry.
Doyle returned with several other guards to Los Angeles with Merry.
Meredith realizeed that Doyle had maintained control of the guard and was disappointed with her for not using the alliances she fought hard to gain.
Doyle also realized that his attempts to remain mysterious by absenting himself from Merry's bed backfired. Merry had only grown closer to her other lovers, allowing her Darkness to become remoter.
Andais revealed to Merry that the true reason she never took Doyle into her bed was for fear he would be king in truth, not merely in name.
Along with the other guards, Doyle helped Merry defeat the Nameless.