The theme of this movie, Nimoy said, is communication. Various problems and barriers to communication are in every early scene. We see the Klingon ambassador making his case for Kirk's villainy before the Federation President and Council, reciting the basic facts---which constitute much of what occurred in Star Trek III--- with just enough distortion and skewed interpretation to change their meaning completely. It's an object lesson in point of view and ideological warp that's just as relevant in the Red States/Blue States USA of today as it was in the Cold War 80s.

On Vulcan, while Scotty and crew struggle to translate Klingon symbols and adapt the foreign language of an alien spacecraft's operation, the reborn Spock is testing his memory, which is as sharp as ever. It's his communication skills that are lagging. He can answer complex mathematical questions but not "How are you?" His mother suggests his human emotions aren't communicating with his Vulcan mind, but they will need to if he is to communicate with his human shipmates. In essence, she sends Spock on the journey he will take in this film: assimilating his humanity.

Though Leonard Nimoy says he had trouble acting and directing in the same movie and feels his Spock characterization suffers as a consequence, his performance perfectly serves a character arc. This Spock is emotionally innocent, free of the internal conflicts of his alienating personal history that he fought to control, suppress and eventually transmute before his "death." Now he is a reborn innocent, and Nimoy plays his personal journey with eloquent economy.

After the Enterpriseless crew heads back to earth in the captured Klingon Bird of Prey to stand trial for disobeying orders so they could save the Federation---an extreme difference in interpretation if not utter miscommunication---they confront the key problem in communication that will drive the subsequent action. The earth is about to be destroyed by a very powerful probe, that looks a little like the one that threatened earth in Star Trek: The Motion Picture (by the shape and color, like V'ger indeed), and also kind of like a whale (yes, very like a whale).

By listening to the sounds it emits, Spock is somehow able to ascertain that this probe represents an unknown form of energy of great power and intelligence that is attempting communicate. Though not hostile, it is somehow unaware of the havoc it is causing on the planet below. How does he know this? Simple logic. Or from reading the script. Spock knows these things, and his analysis often includes the word "unknown," which is one of those signals that this is Star Trek.

"Oh, really?" McCoy the skeptic says. "You think this is its way of saying 'hi, there' to the people of the earth?"

"There are other intelligent forms of life on earth, doctor," Spock replies with Vulcan acidity. "Only human arrogance would assume the message must be meant for man."

Before Star Trek II, DeForest Kelley had to explain to Harve Bennett exactly how the Kirk-Spock-McCoy relationships work, and how central they are to Star Trek storytelling. By this time Bennett had learned the lesson well. At this point in the story, McCoy and Spock have already had a memorable and elegantly written exchange on the subject of death. McCoy expressed disbelief when Spock declined to discuss his experience of dying because McCoy hadn't died himself so they had no common frame of reference, but saw that he was serious. Their conversation was interrupted by messages Spock was monitoring. "Forgive me, Doctor, I'm receiving a number of distress calls," Spock said. "I don't doubt it," McCoy replied.

McCoy has been openly skeptical of Spock's fitness so soon after his ordeal. But what came off as scowling and rasping alarmism in the first film as in some TV episodes, is played here perfectly as waspish, sardonic critique. Earlier, Kelley delivered a line that harkened back to the old Saturday morning space operas while still being perfectly McCoy. Referring to Spock, McCoy stage-whispered to Kirk, "I don't know if you've got the whole picture or not but he's not exactly working on all thrusters."

But Spock has now quickly gotten to the heart of the dilemma. The humans below cannot respond to the message because they can't understand it, and they can't understand it because it's not meant for them. Spock notes that the alien transmission is aimed at the oceans. In one of those quasi-scientific sleights of hand that Star Trek at its best can do so well, Uhura fiddles with some dials and reproduces the alien's song as it would sound underwater. It sounds very like a whale.

But it's the 23rd century, and because of human unconsciousness---or stupidity allied with cupidity---in the 20th century, there are no humpback whales to answer. Since 20th or 21st century humans didn't manage to translate the whale's song, or didn't try to, before extinguishing it forever, they will have to find some actual whales, where and when they are. McCoy's delayed reaction when he realizes that Spock's suggested course of action implies time travel is another priceless comic moment. Lacking a better alternative, Kirk propels them forward, into the past.