Erin's (Drew Barrymore) wry wit and unfiltered frankness charm newly single Garrett (Justin Long) over beer, bar trivia and breakfast the next morning. Their chemistry sparks a full-fledged summer fling, but neither expects it to last once Erin heads home to San Francisco and Garrett stays behind for his job in New York City. But when six weeks of romping through the city inadvertently become meaningful, neither is sure they want it to end. And while Garrett's friends, Box (Jason Sudeikis) and Dan (Charlie Day), joke about his pre-flight calorie-cutting and his full-time relationship with his cell phone, they don't like losing their best drinking buddy to yet another rocky romance. At the same time, Erin's high-strung, overprotective married sister, Corrine (Christina Applegate), wants to keep Erin from heading down an all-too-familiar road. But despite the opposite coasts, the nay-saying friends and family, and a few unexpected temptations, the couple just might go the distance.