The Fae criminal element has been quiet in Glasgow of late. Detective Inspector Leah Bishop and her Victorian selkie partner, Dorian Grey, respond to a woman's last moments in a Bridgeton close. They discover that an age-old sickness is spreading throughout the city, a silent killer. Caledonia Interpol decides to send Leah and Dorian into the Scottish Highlands to keep her safe. Their winding route through the isolated mountains finds Leah face-to-face with old monsters, new friends, and a love that has outlived plague, pain, and death. When Leah succumbs to the illness, Dorian must race against time to save her, and face memories he'd rather leave in the past.