What is "jump the shark"

vb. (context idiomatic of a television program or other narrative English) To undergo a storyline development which heralds a fundamental and generally disappointing change in direction.

"Jump the Shark" is the 15th episode of the ninth season of the American science fiction television series The X-Files. The episode first aired in the United States on April 21, 2002 on the Fox network. It was written by executive producers Vince Gilligan, John Shiban and Frank Spotnitz, and directed by Cliff Bole. The episode is a "monster-of-the-week" episode—unconnected to the series' wider mythology—and was created to give closure for The Lone Gunmen television series, which was a spin off of The X-Files. The episode earned a Nielsen rating of 5.1 and was viewed by 8.6 million viewers. The episode received mixed to negative reviews from television critics.

The show centers on FBI special agents who work on cases linked to the paranormal, called X-Files; this season focuses on the investigations of John Doggett ( Robert Patrick), Monica Reyes ( Annabeth Gish), and Dana Scully ( Gillian Anderson). In this episode, Doggett and Reyes attempt to locate a female friend of The Lone Gunmen after former Area 51 Man-in-Black Morris Fletcher appears and claims that she is actually a super-soldier. What Doggett and Reyes soon discover is a bizarre plot to unleash a biological weapon via the use of grafted shark organs.

"Jump the Shark" features the death of The Lone Gunmen—popular recurring characters who first appeared in the first season episode " E.B.E.", although this plot was later retconned in the comic book series The X-Files Season 10. The episode proved difficult to make because, after the cancellation of The Lone Gunmen television series, Fox was adamant that the characters not have a featured role back on The X-Files. (The characters did appear in four previous season 9 episodes, but always very briefly.) The choice to kill off the trio was controversial. Writers Spotnitz and Gilligan later revealed some regret with the way the episode was handled. However, actors Bruce Harwood and Dean Haglund were happy with the way the episode ended. The episode title is a humorous reference to the phrase " jumping the shark", which is used to describe shows that are in decline to try a gimmick to get attention.