Heading home to face charges, Kirk's crew travels to 1986 San Francisco to find humpback whales that can answer an alien probe devastating Earth.
Star Trek IV: The Voyage Home, released in 1986 and directed by Leonard Nimoy, opens with Kirk and his crew flying home in a captured Klingon ship to face charges over their actions in the previous film. An alien probe has reached Earth, and its signal knocks out power and begins vaporising the oceans, plunging the planet into crisis.
Spock works out that the signal is the song of humpback whales, which are extinct by the twenty-third century. The crew slingshots around the Sun back to 1986 San Francisco, where with the help of marine biologist Gillian Taylor they obtain two whales and carry them to the future to answer the probe.
The film's comedy and environmental message made it a major hit. At its end Kirk is demoted to captain and given command of the new Enterprise-A.