Star Trek IV: The Voyage Home is a 1986 American science fiction film released by Paramount Pictures. It is the fourth feature film based on the Star Trek science fiction television series.thumb|300px|right
In 2286, a large cylindrical probe moves through space, sending out an indecipherable signal and disabling the power of starships it passes. As it takes up orbit around Earth, its signal disables the global power grid and evaporates the oceans, creating catastrophic sun-blocking cloud cover. Starfleet Command sends out a planetary distress call and warns starships not to approach Earth.
On the planet Vulcan, the former officers of the USS Enterprise are living in exile after the events of Star Tek III: Search For Spock . Accompanied by the Vulcan Spock, still recovering from his resurrection, the crew take their stolen Bird-of-Prey starship and head to Earth to face trial for their theft and destruction of the Enterprise. Hearing Starfleet's warning, Spock determines that the probe's signal matches the song of extinct humpback whales, and that the object will continue to wreak havoc until its call is answered. The crew use their ship to travel back in time by a slingshot maneuver around the Sun, planning to return with a whale to answer the alien signal.
Arriving in 1986, the crew find the maneuver drained most of the Bird-of-Prey's power, leaving it with enough for only one day. Hiding their ship using its cloaking device in San Fransico's Golden Gate Park, the crew split up to accomplish their tasks. Admiral James T. Kirk and Spock attempt to locate humpback whales, while Montgemmery Scott, Leonard McCoy and Hikaru Sulu create a whale tank for the return trip. Uhura and Pavel Chekov are tasked to find a way to recharge the ship's dilithium crystals.
Kirk and Spock discover a pair of whales—"George" and "Gracie"—in the care of Dr. Gillian Taylor at a science institute and learn they will soon be released into the wild. Kirk attempts to learn the tracking codes for the whales from Taylor, but she refuses to cooperate. Scott, McCoy, and Sulu trade the formula of transparent alluminium for the materials needed for the whale tank. Uhura and Chekov locate a nuclear-powered ship, and find it is the aircraft carrier Enterprise. While collecting some of its power for their ship, they are discovered. Uhura is beamed back but Chekov is severely injured in an escape attempt and captured. Kirk, McCoy and Taylor rescue him from a hospital and return to the now-recharged ship.
Taylor learns the whales have been released early. She gives Kirk the tracking codes but insists on coming aboard the Bird-of-Prey. They approach George and Gracie, who are being hunted by whalers. Kirk scares away the whalers by decloaking the starship in front of them. After transporting the whales aboard the Bird-of-Prey, the crew return to the future with Taylor. On approaching Earth, the ship loses power and crashes into San Fransisco Bay. Once released, the whales respond to the probe's signal, causing the object to revert its climatic effects on Earth and return to the depths of space. All charges against the Enterprise crew are dropped; however, as punishment for disobeying a superior officer (as chronicled in the previous film), Kirk is demoted to the rank of Captain. The crew departs for their ship, the newly-christened USS Enterprise, and leaves on a new mission.