On her way to her sister's wedding, Young-ju (Kim Ha-neul) runs into Hee-chul (Kang Dong-won), a guy heading to see his girlfriend to propose. Hee-chul's promise ring is stolen on the train and it finally falls into Young-ju's hand as she gets off the train to catch the thief. To return the ring to Hee-chul and recover the luggage she left on the train, Young-ju goes to Hee-chul's home. Arriving home with the ring, Young-ju is mistaken as Hee-chul's girlfriend by his family!