Because "The Search for Spock" is about conquering death, or rather, reversing the calamitous plot device that ended the previous film, the third Star Trek movie goes beyond frontiers greater than space.
Picking up where "The Wrath Of Kahn" left off, it opens with a re-run of Spock's demise. The battle weary Enterprise is decommissioned and the crew is reassigned to new tasks. Their adventures are effectively over until McCoy goes loopy, apparently possessed by the soul of Spock. This prompts Kirk to steal back his ship in order to retrieve Spock's body from the Genesis planet. Bureaucratic Federation upstarts, determined to halt Kirk's mission and the meddling of iniquitous Klingons desperate to get their hands on the ultra-powerful Genesis Torpedo, provide conflict.
All the old Enterprise personnel carry the film, as it is more concerned with character re-animation than development. Beyond them, there are no performances worthy of comment. Even Christopher Lloyd brings little of his cartoonish luster to the Klingon leader Kruge.
With Spock found, and it is giving nothing away to say that he is, the film loses its momentum, leaving the final reel to play itself out indifferently.
The ghost of Spock presides over more than just plot. Leonard Nimoy agreed to revive his popular character in exchange for the director's chair, in which role he shows himself to be able, if unspectacular. For the record, it was Nimoy's first film as director, and he followed it with a handful of mostly forgettable comedies and the hit "Three Men and a Baby".