Friday the 13th is a series of films based around the campingsite Crystal Lake. In 1957, during summer camp, a disfigured boy was bullied by the other kids. It went so far that they drove the boy in the lake. The boy couldn't swim and drowned. The accident could happen because the counselors that should have been looking after the kids, had no attention for them. They rather had eye for each other, neglecting their duties. Due to the nature of the accident and the fact that people responsible for the accident went free without punishment, Pamela Voorhees started to kill the counselors, starting a killing spree that was continued by her son Jason as he returned to Crystal Lake.
The film spawned 9 sequels, and 1 cross-over with A Nightmare from Elm Street and was rebooted in 2009, with Friday the 13th.