Kate (Olivia Wilde) and Luke (Jake Johnson) are co-workers at Chicago craft brewery Revolution Brewing, where they spend their days drinking and goofing off. They seem to be perfect for each other, but they are both in relationships. Kate is with Chris (Ron Livingston), and Luke is with Jill (Anna Kendrick). Jill is a nice and practical girl, whereas Chris is more of an introvert. Jill presses Luke about marriage, which he promises he will be able to talk about some time soon.
One day, Luke and Kate are drinking with co-workers, and Jill and Chris also show up. Chris invites Luke and Jill to join him and Kate for a trip to his family’s cottage. During the trip Jill and Chris go for a long hike in the woods, where they end up kissing.
Luke and Kate spend the whole trip drinking and staying up late alone together, and end up having a bonfire together. Kate invites Luke to go skinny dipping before stripping off her clothes and running into the lake.
After the group returns home, Chris realizes his and Kate’s differences and breaks up with her. Newly single Kate insists the whole brewery crew go out the next evening for drinks to celebrate her ‘singleness.’ That night she ends up sleeping with a co-worker, Dave. When Luke hears about this he is angry at both Dave and Kate and spends the whole day snapping at both of them, but eventually apologizes for his behavior. Jill decides to go away for a week with some friends from college. During this trip, Luke and Kate go out for dinner and fall asleep together on the couch. Luke agrees to help Kate clean out her old apartment and move the next day, and at the end of the day Luke falls asleep on the bed. Kate joins him.
The next morning, Luke and Kate keep moving and make plans to get dinner to celebrate when they are done. Luke cuts his hand badly while helping move a couch. Kate is squeamish about the blood and unhelpful. An impatient driver, blocked by the moving van, yells at them and starts a fight with Luke. After Luke ends up with a broken lip, Kate calls Dave and another co-worker to help finish the move. When Dave invites Kate out for drinks, she agrees to go with him instead of going to dinner with Luke. Luke is annoyed and an argument ensues.
Returning home, Luke finds Jill has come home early, and she is crying. She sees his injuries and while cleaning him up, confesses to kissing Chris while at the cottage. She tells Luke how guilty she feels about what happened, and that she really loves him and wants to marry him. Luke forgives Jill and lets her know that he still loves her and wants to marry her. The next day at work Kate and Luke awkwardly interact and then eventually end up sitting together at lunch. They each offer one another bits of their lunch before they crack a smile, and drink a beer.