Star Trek IV: The Voyage Home

In 2286, Kirk and his friends live in folds exiled on Vulcain, supervising progress of Spock who finds back little by little his memory. Taken between two fires, Kirk finally decides to take the Klingon Bird of Prey and to render on Earth to assume charges retained against him. Spock, who still suffers his fal-tor-pan, decides to accompany his Captain. The crew finds the Earth in full agitation, threatened by a probe coming from outer space on the point to gobble the planet. Starfleet counsels to all vessel approaching the Earth to hold from a distance.

Spock succeeds to identify the unusual form of communication of the probe that resembles the language of whales disapeared a long time ago. The only mean to stop the probe would consists in a reply to its message. Kirk and his crew, in orbit around the condemned planet, thought that the alone manner to save the planet is to return in the pass in 20th century, when whales were still existing, and to bring back specimen of mammals in order that they communicate with the probe...