Jaimie Vane used to measure her life in concert halls and standing ovations. Now she measures it in symptoms. The chronic illness that ended her career as a cellist doesn’t have a name or a cure --- just a long list of things her body can’t do anymore. When her wild child younger sister, Sybil, reinvents herself as a live-in staffer at an ultra-exclusive wellness retreat, Jaimie assumes it’s another phase. Until her messages stop. Until the voucher arrives. Talamh Dhubh, a black-sand island in the middle of a wintry sea and home to Saoghal Spa, is a place for guests to be reborn. The founder, the enigmatic and glamorous Cyan Blache, promises restoration. Jaimie tells herself she’s only there to find Sybil. But the longer she stays, the lighter her body feels. At Saoghal, healing is real. And so is the cost.

After the tragic death of their parents, the seven Ward sisters are sent to live with their grandmother on the remote forest island of Beltane, a place suspended between time and shadow. What begins as an attempt to mend their fractured lives soon twists into a waking nightmare, where grief bleeds into childhood fantasy and ancient rites awaken a dark and eerie devotion to Daudir, the Forgotten God of the Wood. When another cruel tragedy strikes, the sisters are left to fend for themselves. The fragile world they’ve carved splinters beneath the weight of isolation, and the forest around them grows restless. Years later, a cryptic letter summons the surviving sisters home. Drawn back into the wild embrace of their dangerous faith, they confront a truth more terrible than memory, and the dreadful secret that waits in the depths of the all-seeing trees.

With one unexpected email from her estranged best friend, Lucy, Mina Murray’s carefully curated life is turned upside down. Leaving behind her psychiatric practice in London, she returns home to the windswept shores of Wales. Faced with everything she’s left behind, she soon discovers that Lucy’s symptoms mirror those of her mysterious amnesiac patient hundreds of miles away. With nothing but an untreatable sickness connecting the two women, and with Lucy’s life on the line, Mina finds herself asking questions and being drawn ever-deeper into a web of secrets, missing girls, and the powerful, nameless force at its center --- one that has been haunting her for years. As terrible, ancient truths begin to reveal themselves, Mina prepares to confront her own darkest secrets and, with them, an evil beyond comprehension.