Friday the 13th: Mother's Day is based off of the first of four books in the Camp Crystal Lake novel series. The story is set some years after the events of Jason Goes to Hell - The Final Friday.
With Jason in Hell, the area of Crystal Lake has been quiet for some time. People are free to roam the area unharmed, though most refrain from doing so. Joe Travers, a local Hunter, doesn't let himself get worried by the legend and poaches the area. He stumbles upon a marker and makes and incredible find. This find leads him directly to the gates of Hell itself, where he uproots what was laid to rest: the mask of Jason Voorhees, and his evil spirit.
While this happens, Billy Boone organizes a party for him and his friends. And the location? Crystal Lake. He convinces Carly McDonnell to join in on the adventure, even though she knows her mother will be worried sick about her. The group arrives at the lake just in time for Camp Blood to resume operations. One by one The Hunter stalks them, because that's what Jason would do, and that's what Mother wants.