How did
Friday the 13th
begin as a movie about a grieving mother killing camp counselors and spawn a movie in which a nanobot enhanced, hockey masked man destroys a space station? Similarly, how did
A Nightmare on Elm Street
evolve from a film by Wes Craven about Freddy Krueger into a film about Wes Craven making a Freddy Krueger movie?  Film series are destined to change with time, but horror film series are often unrecognizable after multiple sequels and reboots.
This work examines horror films and their sequels to determine the glue that holds individual franchises together, which films matter to a series' continuity, which should be considered as canon, and what goes into the process of continuing—or, in some cases, abandoning—the overarching storyline.  Series covered include
Friday the 13th, Halloween, Child's Play, A Nightmare on Elm Street, Leprechaun,
and
Scream.