Seanan McGuire - October Daye Series

Rosemary and Rue
October “Toby” Daye, a changeling who is half human and half fae, has been an outsider from birth. After getting burned by both sides of her heritage, Toby has denied the Faerie world, retreating to a “normal” life. Unfortunately for her, the Faerie world has other ideas…
The murder of Countess Evening Winterrose pulls Toby back into the fae world. Unable to resist Evening’s dying curse, which binds her to investigate, Toby must resume her former position as knight errant and renew old alliances. As she steps back into fae society, dealing with a cast of characters not entirely good or evil, she realizes that more than her own life will be forfeited if she cannot find Evening’s killer.

A Local Habitation
Toby Daye-a half-human, half-fae changeling-has been an outsider from birth. After getting burned by both sides of her heritage, Toby has denied the fae world, retreating to a "normal" life. Unfortunately for her, the Faerie world had other ideas...
Now her liege, the Duke of the Shadowed Hills, has asked Toby to go to the County of Tamed Lightning to make sure all is well with his niece, Countess January O'Leary. It seems like a simple enough assignment-until Toby discovers that someone has begun murdering people close to January, and that if the killer isn't stopped, January may be the next victim.

An Artificial Night
October "Toby" Daye is a changeling-half human and half fae-and the only one who has earned knighthood. Now she must take on a nightmarish new challenge. Someone is stealing the children of the fae as well as mortal children, and all signs point to Blind Michael. Toby has no choice but to track the villain down-even when there are only three magical roads by which to reach Blind Michael's realm, home of the Wild Hunt-and no road may be taken more than once. If Toby cannot escape with the children, she will fall prey to the Wild Hunt and Blind Michael's inescapable power.

Late Eclipses
October "Toby" Daye is half-human, half-fae-the only changeling who's earned knighthood. But when someone begins targeting her nearest and dearest, it becomes clear that Toby is being set up to take the fall for everything that's happening.

One Salt Sea
October "Toby" Daye is settling into her new role as Countess of Goldengreen. She's actually dating again, and she's taken on Quentin as her squire. So, of course, it's time for things to take a turn for the worse.
Someone has kidnapped the sons of the regent of the Undersea Duchy of Saltmist. To prevent a war between land and sea, Toby must find the missing boys and prove the Queen of the Mists was not behind their abduction. Toby's search will take her from the streets of San Francisco to the lands beneath the waves, and her deadline is firm: she must find the boys in three days' time, or all of the Mists will pay the price. But someone is determined to stop her-and whoever it is isn't playing by Oberon's Laws...

Ashes of Honor
It’s been almost a year since October “Toby” Daye averted a war, gave up a county, and suffered personal losses that have left her wishing for a good day’s sleep. She’s tried to focus on her responsibilities—training Quentin, upholding her position as Sylvester’s knight, and paying the bills—but she can’t help feeling like her world is crumbling around her, and her increasingly reckless behavior is beginning to worry even her staunchest supporters.
To make matters worse, Toby’s just been asked to find another missing child…only this time it’s the changeling daughter of her fellow knight, Etienne, who didn’t even know he was a father until the girl went missing. Her name is Chelsea. She’s a teleporter, like her father. She’s also the kind of changeling the old stories warn about, the ones with all the strength and none of the control. She’s opening doors that were never meant to be opened, releasing dangers that were sealed away centuries before—and there’s a good chance she could destroy Faerie if she isn’t stopped.