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No actual storyline has ever been revealed for this movie, but here's what I came up with:

Stab 7: Knife of the Hunter picks up right where Stab 6: Ghostface Returns left off. When 18-year-old Chloe (Kristen Bell) murders her best friend, the town puts her on trial for the previous Ghost Face killings, which she admits to but also reveals that she has a mysterious partner. As Chloe sits awaiting trial, her partner begins to target the entire town of Woodsboro. With no clear pattern or suspects, Gale (Elizabeth Banks) and Dewey (David Schwimmer) must solve the case the old-fashioned way. All bets are off in the final showdown.   

FUN FACT #1 This film was based on the Gale Weather's book "Knife of the Hunter."

FUN FACT #2 The subtitle "Knife of the Hunter" was never shown in the Scream movies on posters, DVD cases or on screen. It was added on the fan created DVD covers. So, it may not actually be part of the title of the film.

FUN FACT #3 The original title of both the book and movie were "Under the Mask" before it was changed to "Knife of the Hunter." Some fan created promo artwork still exists with the old title on it. 

FUN FACT #4 In Scream 4, it was stated that Sidney threated to sue the studio if they used her story after Stab 3, so it's safe to assume that the Sidney character wasn't used again. However, in Scream 5, the killer says “Sidney was in all the Stab movies, except the last one.” So, who's right? We don't know and apparently neither do the writers of the Scream movies.