Star Trek IV: The Voyage Home

While back on Earth, standing trial for their hijacking of the starship Enterprise (see STAR TREK III), Kirk and his crew are thrust into a new adventure. A space probe threatens to destroy the planet if it is not allowed to continue its longstanding communications with a certain species of Earth mammal -- humpback whales. Unfortunately, there is an obstacle to their simple demand; the whales are extinct in the 23rd Century. So Kirk, Spock and the gang travel back in time to San Fransisco, circa 1986, where they battle culture shock, as well as the clock, while trying to corral a few friendly whales to bring back to the future. (official distributor synopsis)