Joel wakes up, seemingly trying to remember where he is.
Outside, there is a huge dent on his car door, which he assumes the driver who parked next to him is responsible for. It’s Valentine’s Day 2004. While waiting for his train to downtown New York, on impulse, he decides to run to the other platform and catch the train to Montauk instead.
The beach is cold and deserted. But he comes across a woman, whom he later runs into at a diner and on the train back. Thus, Joel and Clementine meet*.
*(spoiler): and in fact not for the first time in their lives.