Star Trek IV: The Trial of James T. Kirk

Star Trek IV: The Trial of James T. Kirk was the proposed fourth film in the original Star Trek film series, following on from 1984's Star Trek III: The Search for Spock. The screenplay was written by Steve Meerson and Peter Krikes, based on a story by Harve Bennett, who had produced and co-written the previous two Star Trek films.

Plot
Following the events of the previous film, Admiral James T. Kirk returns to Earth to stand trial for his actions in the previous film, including stealing and later destroying the USS Enterprise. The trial also brings him face-to-face with several of his past foes, including Harry Mudd, Klingon commanders Kor and Kang, and the Romulan commander he unwittingly abducted during a mission to steal her ship's cloaking device. During the course of the trial attempts are made on the life of both Kirk himself and several Federation officials, leading the other Enterprise crew members to believe that one of the prosecution witnesses may be trying to settle an old score.

Why It Was Cancelled

 * 1) Paramount didn't like the story, firstly feeling that a legal drama and whodunnit was a poor fit for the Star Trek film series, and secondly that it was time for a more fun and light-hearted Star Trek film, after the death of Spock in the second film, and then the death of Kirk's son, David Marcus and the destruction of the USS Enterprise in the third film.
 * 2) The writers were having trouble making the story work, since Kirk was very clearly guilty of the crimes he was being accused of, forcing them to resort to the assassination plot to bring the story up to length. On top of that, the combination of Kirk being on trial and a whodunnit plot had already been done on the TV series, in the episode "Court Martial".
 * 3) There were concerns about getting all the various guest stars back for the film - in particular, Harry Mudd's actor, Roger C. Carmel, was seriously ill and ended up dying before the release of the actual fourth film - as well as worries that casual moviegoers might not know who the characters were.
 * 4) Finally, when Leonard Nimoy agreed to return as director after his successful debut on the previous film, he only agreed to do so if he could make an pro-environmental story that had the main characters travel back to the 20th century.

Results

 * 1) Nimoy's idea eventually became the film Star Trek IV: The Voyage Home, which proved the biggest critical and commercial success of the original cast Star Trek films. It still incorporated the idea of Kirk being on trial, but only for a single scene during the film's ending.
 * 2) Kor and Kang, who had been set to cameo in the film, would later appear (along with a third TOS Klingon, Koloth) in the TV series Star Trek: Deep Space Nine.