In 1814, three cousins—Gretchen, Emma, and Penelope—discover their unknown family lineage of witchcraft when their individual magical powers unexpectedly begin to manifest. Now, beyond the familiar manicured gardens and ballrooms of Regency London, a dangerous, alluring underworld available only to those with power is now open to the cousins.

But by claiming their power, the three cousins have accidentally opened the gates to the Underworld. Now ghouls, hellhounds—and most terrifying of all, the spirits of dark witches known as the Greymalkin Sisters—are hunting and killing young witches for their powers. And, somehow, Emma is connected to the murders ... because she keeps finding the bodies. Can the cousins seal the gates before another witch is killed ...or even worse, before their gifts are stripped away?