A group of strangers are invited to Shambala, a remote winter resort, for the New Year's Eve festivities. One person, however, has plans that don't involve celebrating.

Tensions build between Nick/Bobby and Chris/Adam. Everyone discusses how they ended up in Shambala. An exploration of the caves finds an unlikely source explaining why they are all there.

Nick confronts Emma, and Dr Serob explains his relationship with Alex. Meanwhile - The search above ground begins after both Preston and Ophelia receive worrying information about their children.

Bobby swears revenge over the death of his friend. Concerned about her husband, Marie goes in search of Chris. Bobby confronts the others about Nick's death and everyone splits up unsure whom to trust. Bobby seeks an alliance with Emma.

The search continues with Preston enlisting powerful allies. With their supplies destroyed, the group has to decide their next step. After waking up with a gun beside him, Bobby wants answers. Dimitri is caught in a trap set by their host.

Marie is not doing well underground. Lisa and Kat decide to join Bobby and the trio makes a startling discovery. More discoveries are made as to why each person is there and their relationship to the death of Alex.

After the death of Kat, Lisa is left alone with Bobby. Without medication, Dimitri's condition continues to deteriorate. Ophelia and Inspector Popa hit a dead end and decide to go to the press, but Preston recognizes a name.

Two different views of the puzzle leave Bobby and Lisa wondering what is next. Marie searches for answers and Emma's truth is finally revealed, forcing Chris to confront the demons of his past.

It's eight years earlier, and we finally see what really happened that fateful night, as Chris comes clean to Marie and the others. Two members of the group find themselves in dire trouble while one manages to escape.

A fallen matchstick confirms that the hatch has been opened, validating Marie's letter to Chris. Meanwhile, much to Preston's horror, something has returned for Vivian, speeding up the already ticking clock to find their son.

Lisa is in trouble as Bobby shows his true colors again. The rest of the group takes issue with Serob's frequent disappearances, but soon learns that he's not the killer. Meanwhile, Jessica's grasp on reality is heading down a dark path.

Emma shares her secrets with Jessica. Desperate to find his son, Preston gives a press conference and offers a reward for information. Nora takes Bobby up on his offer, but her heroics end in rage as the others learn the cost of the deal.

Lisa tries to escape from Bobby's grip. Whilst Preston is left to confront his new reality, the Inspectors follow the trail of witnesses. Meanwhile, Chris and the others deal with Jessica, before going after Bobby.

With no doctor to help, another captive falls. Things between Bobby and Lisa continue to approach boiling point. Above ground, the bodies continue to pile up, whilst below, an emotionally unstable Jessica finds an important item.

As the group makes a discovery about the gun, the Inspectors locate Shambala, and call on Preston's influence to get them there quickly. Preston reveals more about that fateful night, and below ground, the mastermind is finally revealed.

With the final revenge for Alex's death in sight, the group learns the last pieces of the puzzle. The guilty are exposed, and sacrifices are made to determine who escapes from Purgatory, and who is left behind to pay for their sins.