Gene Roddenberry's original Star Trek 'family' fully expected that Paramount would 'pull the plug' and end their series of films after STAR TREK III: THE SEARCH FOR SPOCK. After all, Spock had died and been reborn, Kirk and the crew were fugitives from the Federation, and the Enterprise itself had been destroyed, with the cast, now the proud owners of a Klingon 'Bird of Prey', staying with Spock's parents, Sarek and Amanda, on Vulcan. Pretty heady stuff for a franchise considered past it's prime, and as the studio seemed to be focusing it's attention on the upcoming 'Star Trek: The Next Generation' television series, which would introduce a younger cast, there was a general feeling that the aging veterans of the first series, now all in their fifties and sixties (with the exception of George Takei, a 'kid' of 46) were overdue to be 'put out to pasture'.
But producer Harve Bennett and Leonard Nimoy had an idea for a 'Trek' film that would be 'hip', lighter-hearted, could 'tie up' the loose ends of the series, and, as the film would be set largely in the 20th century, be both inexpensive to make, and 'audience friendly'. "Inexpensive" was always the key word for Paramount's 'brass', particularly concerning 'Star Trek', and after Bennett and Nimoy made the rounds pitching their script outline, and Nimoy agreed to direct, the project was green-lighted.
The story is simple and straightforward; returning to Earth in the 'Bird of Prey' to face charges for hijacking the Enterprise, and destroying it, Kirk and crew discover that the planet is 'under attack' from a gigantic tube-like object, emitting weird sounds and laser-like beams that are playing havoc on the weather, world-wide. Spock determines that the sounds are the language of humpback whales, a species extinct in the 23rd century, so our heroes slingshot the spaceship back in time to the 20th century, in an attempt to capture a pair of the whales, and bring them 'back to the future'.
As the Klingon ship has a cloaking device that can render it invisible (a wonderful invention that helped keep the FX budget down!), it is easy to 'hide' the spacecraft in a park in mid-eighties San Francisco, and the crew, after a funny sequence strolling the streets of the city, are divided into teams, with Kirk and Spock to procure the whales, McCoy and Scotty to build a tank to house them, Sulu to find a means of getting the tank to the ship, and Uhura and Chekov to siphon off some nuclear fuel (from the U.S.S. Enterprise, no less!) to help power the ship back to the 23rd century. Each team has their own mini-adventure (Kirk and Spock meet whale expert Dr. Gillian Taylor, played by perky Catherine Hicks, who, eventually, insists on accompanying the whales to the future, while sweetly shrugging off Kirk's passes; Scotty has to 'invent' the glass for the tank, potentially rewriting the future; Sulu is like a kid, flying an antique helicopter; and Chekov gets captured, then injured...Chekov is ALWAYS getting injured in the 'Trek' films!...providing McCoy a chance to perform some 'miracles' and criticize 20th century medicine). These vignettes are wonderful, and remind one of what terrific actors the original crew of the Enterprise were.
The Earth is, of course, saved, Kirk is busted from Admiral back to Captain (the rank he was best suited for), Dr. Taylor informs him she's too busy to date (Kirk strikes out???), and the crew is assigned to a new starship...named Enterprise, naturally!
STAR TREK IV, the most popular and successful 'Trek' movie yet made, would have been a fitting conclusion to the adventures of the original cast, but William Shatner, as part of his contract, was promised a writing credit and the director's chair for the next 'Trek' film...