Sergeant Jackie O'Hara arrives on the remote Isle of Toll Mòr to follow up an emergency call from local farmer Frank Guthrie. As the weather worsens and she makes her way inland, nothing can prepare her for what she's about to witness
The storm closes in and Jackie desperately searches for the missing girl. As Holy Wednesday turns to Maundy Thursday, a stranger is discovered near the Ward farmhouse.
With the search effort frustrated, Jackie reads the old book Father McKenna gave her telling of an ancient and horrifying prophecy. On the other side of the island, Twig questions Kai, while he makes preparations for battle
The arrival of a military rescue team on Good Friday buoys the islanders. Jackie joins Major Tanner and his troops as they set out across the inhospitable landscape to track down Kai and rescue his captive, Twig.
After the battle, Kai is captured by Tanner. A shocking revelation makes Jackie question everything she knows. With her allegiances torn, she risks her life to protect Twig and the islanders.
The final confrontation looms. The great evil that has engulfed the island threatens a brutal revenge and Jackie finally comes to understand the terrible truth of what is happening on Toll Mòr.