When Star Trek: The Motion Picture debuted in December of 1979, many fans were disappointed by what they saw on the big screen. While Kirk, Spock, and the rest of the Enterprise's crew were presented in larger than life fashion, The Motion Picture was a relatively ponderous affair that spent more time watching ships travel the galaxy than actually doing anything interesting. It was Star Trek -- just Star Trek minus many of the things that made the original series so beloved. This didn't stop Paramount from going back to the drawing board, though. For the 1982 sequel, they booted series creator Gene Roddenberry and restored the adventure elements sadly missing from the original film. The result was The Wrath of Khan -- a title that is arguably the greatest movie in the Star Trek canon -- and a quintessential summer movie experience thanks to its blend of large-scale action set pieces and nifty (for the time) visual effects. Star Trek II had a story, but it wasn't particularly deep -- a perfect example of the "shut off your brain" mentality that has come to characterize films released between early May and late August.
The sequel is a follow up to the episode Space Seed, where Kirk squared off against Khan Noonien Singh (Ricardo Montalban and his hair). Khan and his followers wound up exiled on Ceti Alpha V, but The Wrath of Khan picks up 15 years later, with the crazy villain hellbent on getting revenge against Kirk.