A Lesson in Thorns (Thornchapel, #1) by Sierra Simone

From the author of the USA Today bestselling Priest and New Camelot series comes a high-heat, gothic, dark academia fairy tale full of lantern-lit rituals, foggy moors, and obsessions that last for a lifetime.

Twelve years ago, she left Thornchapel—and the two boys she gave her heart to—behind.

Now, Proserpina Markham has returned, hopeful…and wary. Because it's so very easy to be drawn back into the world of the seductive and elegant Auden Guest…and into the world of his worst enemy, St. Sebastian Martinez. The beautiful and brooding St. Sebastian is as irresistible as he ever was, and Auden is just as handsome and arrogant, and the three of them can't seem to unknot themselves from each other.

From the hasty promise they three made all those years ago.

As Thornchapel slowly tightens its coil of truths and lies around them, the reluctant threesome starts unravelling into filthy, holy pleasure and pain. Together, they've awakened a centuries-old fate that will either bloom like a rose…or destroy them all.