Mary (Moon Geun Young) doesn't even have any experience dating, but somehow she ends up in contract marriages with two guys! In order to clear his debts, Mary's irresponsible father (Park Sang Myun) decides to marry her off to his rich friend's son Jung In (Kim Jae Wook), the boss of an entertainment production company. Taking matters into her own hands, Mary forges a fake marriage contract with her new friend Moo Kyul (Jang Geun Suk), a free-spirited indie band singer who never stays in relationships for long. But Mary's father has his own countermeasure: he registers Mary and Jung In's marriage without their knowledge! To appease the parents, the reluctant bride and grooms agree to a 100-day trial period in which Mary shares her time between her two husbands, neither of whom are interested in marrying her. But a lot of things can change in 100 days, including feelings! Moo Kyul or Jung In, who is really the one for Mary?