Right when Audrey is about to kill Nathan for the greater good of Haven, she looks up to see one of the devious henchmen that haunted her inside The Barn. She and Nathan give chase and run into Duke, Vince and Dave who are rushing in to make sure that Audrey hasn't already killed Nathan.
Now that the henchmen have escaped from The Barn into the real world, everything has changed and if Audrey kills Nathan, the whole town will be sent into a tailspin. Meanwhile, the henchmen are doing their best to rip the town apart by amplifying the power of the Troubles as well as infecting people with rage and paranoia.
The henchmen kidnap Dwight and hold him hostage but he manages to sneak in a call to Nathan who shows up with Audrey to save him. Once they free Dwight, they discover another prisoner: William, the man who helped Audrey escape from The Barn. After they get William to the police station, they discover that he has amnesia. He doesn't remember who he is or how he was captured but Audrey remembers William fondly and she helps him remember how he helped her in The Barn.
Elsewhere in the prison, the henchmen use their powers to infect Dwight, Jennifer and Nathan with a rage-like paranoia. Since things are falling apart amongst their core group, Audrey and Duke lock Jennifer, Dwight and Nathan up. Later, when Audrey and William leave to set things right in the town, Duke stays behind to stand guard.
Later, when Audrey and William touch some of his memories come back. In fact, he's able to lead Audrey right to the box that the henchmen were interrogating Dwight about. Unfortunately, it's not all good news. He also reveals himself to be the boss of the two henchmen and claims that he and Audrey had a significant relationship sometime in the past. So, William never actually lost his memory. It was all a ruse to help Audrey remember him and the time they previously shared together.
Now that William has played his hand, Nathan, Jennifer and Dwight return to normal (much to Duke's relief) but William still has Audrey trapped in the middle of nowhere and it's three against one. William knocks Audrey out and, when she awakens, fortunately, Nathan is there to comfort her.
Colin Ferguson gives his final thoughts on the season finale of Haven.
In Haven's fourth season finale, William's plan to turn Audrey back into her original self, collides with Audrey, Duke and Nathan's plan to trap William back in the dark place he came from.
Get a look at the references to Stephen King's works from the season 4 finale.