An unstoppable disease.

A fanatical doctor.

A nightmare obsession.

As a deadly plague rips through Harriet's village, unexpected salvation arrives in Adam: the bright-eyed novice healer with a hidden gift, who vanishes as quickly as he came. Haunted by weird nightmares and a witch's dying words, Harriet seeks the truth about Adam and his mysterious home at Wolfern Priory.

But the world of healers is changing. The royal doctor Lady Hawkes is on a quest to perfect humanity, with her miraculous and addictive new treatment: the Mordant Sleep.

Swept along by dark rumours, guilty secrets and ancient powers, Harriet is drawn into the shadowy conflict between Mordancy and medicine, and finds that perfection can be deadlier than any plague.