Morgan Tenpenny has retreated from her painful, magical past, choosing to live quietly as a guardian of one of the gates between worlds. But her sister Gwen is married to a lord of the High Court of Faerie—and when Gwen asks her to protect her nieces, it's time for Morgan to emerge from her seclusion. The gates to Faerie have inexplicably closed, and no one knows why, not even Falcon, the fae Morgan finds trapped on her side of the gate. As a devastating illness that only affects magic users starts to sweep through the country, Falcon tells Morgan of a way to reach her nieces in Faerie through a mysterious place called Strangehold—if Morgan can trust that Falcon is all that he seems. But with the Queen of Faerie increasingly defensive of her borders, even their combined powers may not be enough to win them through. With relations between fae and human falling apart and a deadly illness threatening all of her old colleagues, Morgan finds that her past isn't as dead as she'd thought. She must navigate the threats in time to save her nieces—and just maybe the world.

Orphaned during the Savannah Flu, Javier is looking for other spellcasters without knowing if any survived. When he finds a caster named Morgan and her nieces, Igraine and Iliesa, he has to hide the secret of his isolated upbringing, desperate not to alienate the only community he has left. But Igraine and Iliesa have secrets of their own. The wild hunt comes to the mortal world seeking them. Why the Queen of Faerie wants them, no one knows, but no one wants to hang around to find out. Javier flees with them between worlds, finding a rare talent for communicating with fae creatures—though he's sure his father wouldn’t have approved of his new hellhound. A mysterious man claiming to be from his mother's estranged family finds Javier, but does he want to claim the family his mother repudiated? He must choose whether to go to his mother's family or help his new friends—but it may be too late to escape the malevolent gaze of the Queen of Faerie.

Faerie is crumbling. When the queen of Faerie closed the gates between Faerie and the mortal realm, a blight on the land began. Now, the fae are turning into twisted versions of themselves as magic is going wrong or vanishing entirely and if the blight goes unstopped, it might spread to Earth as well. Twin daughters of a fae lord and the human ambassador to Faerie, Igraine and Iliesa just want to reunite with their parents and go home to Faerie. But the queen believes that only they can put things right—by becoming a willing sacrifice at Midwinter. The queen has their parents and all the power of Faerie on her side. The twins have their aunt Morgan, the former assassin Rowan, and the young human spellcaster Javier. As the clock ticks down to Midwinter, the twins discover unsuspected links to the land. But when Iliesa tries a desperate spell, she turns the blight onto herself. Bereft of her sister for the first time in her life, Igraine must turn to powers beyond Faerie or Earth for any hope of saving her sister and her homeland. Even if she succeeds, will she recognize what she's become?