It's Earth Day once again. And to celebrate, StarTrek.com takes a loving look back at the most pro-environmental Star Trek film of them all: Star Trek IV: The Voyage Home. The plot came down to this: save the whales, save the world. Man, in the future, had long ago driven humpback whales to extinction and now, ironically, it would take the lyrical whale calls of George and Grace in 1986 to save the future. So, with some sci-fi magic—the slingshot effect (a/k/a light-speed breakaway factor) -- Kirk, Spock and the Enterprise crew landed in San Francisco and engaged in an entertaining, often funny, thought-provoking trek into our (then-) contemporary world.