Everything seems to be going well for Alex—she has her dream job as an intern on a popular investigative news program and is engaged to a man who is almost too perfect. Now her best friends are taking her on a surprise bachelorette weekend planned with Alex's unusual set of interests in mind: her obsession with the famous 666 Killer.

Alex and her friends get a thrill out of staying at the allegedly haunted hunting lodge in the Catskill mountains where a serial killer once stabbed his victim and wrote 666 on the walls in her blood. Though getting snowed in by a blizzard wasn't part of the plan, the three girls make the most of their celebration. Then Alex wakes up to find her friends have vanished, blood spattered all over their sleeping bags and on her hands. With no idea what happened, Alex worries the decade-old murder has come back to haunt them and she is the one to blame. Her recent prison interview with the 666 Killer seems to have stirred up past demons, throwing her friends into danger. The prisoner has always maintained his innocence, claiming the "real killer" was still out there. Has the true 666 Killer finally returned? Alex must rely on her years of following true crime stories to try to solve the case and save her friends. But even she does not see the final, staggering twist coming, and the shocking truth just might kill her.