Kirk goes looking for a rotting corpse and ends up getting a brain-dead body. McCoy gets possessed by a ghost, and at the end everything is right as rain.
Star Trek IV: The Voyage Home
Kirk and Spock wander around 1986 San Francisco looking for whales. Scotty, McCoy, and Sulu wander around looking for plexiglass. Chekov and Uhura wander around looking for nuclear wessles. Guess who ends up being interrogated by the CIA (but I'm sure JJ Abrams would say it was really S.D. 6)?