Niles (Andy Samberg) and his girlfriend's relationship has come to an end, but even so, he still reluctantly followed her to a wedding. At the wedding, Niles, who didn't know anyone, was bored. A bohemian girl named Sarah (Cristin Milioti) attracted Niles' attention. Sarah is the bride's sister. In fact, she and the groom have maintained a physical relationship for a long time. Even the night before the wedding, she spent it in the groom's bed! Such a girl who makes the whole family feel headache is particularly attractive in Niles' eyes. After breaking up with his girlfriend, Niles and Sarah gradually come together. Sarah's hot personality brings surprises to Niles' life, but also creates all kinds of troubles. When Niles finds that he really loves Sarah deeply, the latter leaves without saying goodbye.