Admiral Kirk and the Enterprise visit the ocean-world of Akkalla for diplomatic reasons. Soon Spock and Chekov become lost. A civil war and secrets under the water threaten the entire planet and the Enterprise.
Weinstein had met with Leonard Nimoy, director of Star Trek IV: The Voyage Home, while Nimoy was developing the story for the film. The two discussed, among other things, the idea of using whales, or creatures similar to whales, something later seen in both that film as well as Deep Domain. Weinstein has commented that, "To this day, I don’t know if whales ended up in ST:IV partly as a result of my suggestion, or whether they’d already decided that. But they were nice enough to give me that “Thank you” credit".