The primary theme of T.C. Boyle's "Greasy Lake" is the journey that people take to their own dark sides, although the propensity of males toward violence is also a theme. The story begins with three men heading out for an adventure that soon goes wrong.
When "Greasy Lake" begins, the narrator and his two friends, Jeff and Digby, are about to go home for the night, but instead decide to stop at Greasy Lake for some excitement. They have visions of being "bad" boys, but these visions usually stop with a (mostly) harmless prank.
This night at the lake goes wrong when the young men lose their keys and then almost kill a "bad greasy character" before going on to rape his girlfriend. The journey from prankster to criminal and rapist is a quick one that changes them forever. Another car approaches the lake, so the boys head into the night.
The narrator hops into the lake to escape discovery, not expecting the terrifying experience of running into a dead body. Even after the boys have come back to shore, found their keys and headed home, they have taken a trip through the darker elements of their own masculine nature, as stated in Changing Lives Through Literature.