Susan has always taken comfort in the peaceful rhythm of life on the Isle of Wight. But when her daughter Zoe invites her to a Halloween ghost walk at a remote castle, Susan has a sense of foreboding she can’t quite shake. 

It’s meant to be a bit of fun for the group of old school friends, the thrill of an overnight stay behind the castle’s ancient gates. But when one of them is found dead, the weekend away takes a sinister turn. With the castle locked down and the group trapped inside, it soon becomes clear the killer would have been amongst them. 

As the police begin their investigation, Susan can’t stand by and watch. She knows her daughter, and she knows Zoe’s friends – none of them could be capable of such a terrible act. Could they?