Half a science-fiction adventure and half a timely plea for whale conservation, this adventure of the Starship 'Enterprise' shows the formula wearing pretty thin despite four credited writers.

Returning to earth to face court martial, Kirk and Co find the planet in a state of panic thanks to the presence high above of a paralysing probe trying to communicate with a species of whale that's extinct.

Kirk and his crew travel back in time (conveniently to 1986) when the whales still existed and find a pair in a San Francisco aquarium that are about to be booted off to Alaska where whale-hunters abound.

This makes for a reasonably tense, if slightly over-extended climax and, if not much is made of the invaders' bemusement in 20th century America, the camaraderie of the cast does produce some nice lines and reactions.

Catherine Hicks, a spirited American version of Susannah York, is a refreshing younger face among the collection of affectionately remembered friends.