When Duke goes searching through his family’s diary, he finds an obituary for his grandfather Roy Crocker, along with a note that Sarah killed him. Eager to help Audrey fight her fate, Duke decides to investigate. He finds that Mr. Mosley, a name he also found in his journal, is still alive and living locally. When Duke approaches him, Mr. Mosley gets alarmed and somehow transports Duke to 1955.
It doesn’t take Duke long to find the local bar and get a strong drink. When a fight breaks out in the bar Duke saves the bartenders life but is promptly arrested because he looks like an outsider. After “Junior,” the bartender, vouches for him, Duke is released and sets out to find the younger version of Mr. Mosley. Since he can’t find Mr. Mosley or Sarah, he uses the Worldwide Post to deliver a letter to Audrey 60 years in the future.
Back in the modern day Haven, things are changing rapidly because of Duke’s trip back in time. Not only are Vince and Dave dead, but the Haven Herald doesn’t even exist. Once she gets Duke’s letter from the past, Audrey and Nathan head over to Mr. Mosley’s current residence. Once again, Mosley gets upset and sends Nathan back into the past too.
Nathan finds Duke at the local bar and the two of them start conspiring to get back to the right era. The plot thickens when Nathan asks Junior his name and realizes that the bartender is actually Duke’s grandfather, Roy Crocker. Nathan convinces Duke that he needs to kill his grandfather to prevent the changes that are taking place in the modern day Haven.
Looking for clues, Nathan heads down to the police station to see if an imprisoned member of The Guard can provide any info. Sure enough, Nathan learns that Mr. Mosley is set to arrive via ferry later that same day and Roy Crocker, it seems, is supposed to kill him. When Roy refuses, a police officer pulls a gun on him and Duke saves Roy’s life again.
When Mosley does show up, he’s in the care of Sarah, who is the spitting image of Audrey. Duke and Nathan split up: Nathan goes to visit Mosley and Duke chases after his grandfather. While talking to Mosley, Sarah finds him and throws him out of the hospital. Nathan, as smitten with Sarah as he is with Audrey, soon finds himself out on a date with the lovely, young nurse. Meanwhile, Roy finds the older version of his own journal in Duke’s possession and freaks out.
Despite all their efforts to derail the events of the past, when Roy sets out to kill Sarah before she can kill him, he sets in motion a chain of events that results in Sarah killing Roy just as she was supposed to. This sets everything as it should be and, once Sarah convinces the young Mr. Mosley that he has nothing to fear, he feels better and sends Duke and Nathan back to modern day Haven.
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.