Jang Na Ra and Park Jung Chul add a new and unconventional page to the modern fairy tale in the romantic comedy Oh! Happy Day. Jang Na Ra stars as Hee Ji, a hot-tempered girl with a strong sense of justice. She bursts into a club to stand up for her friends who were rejected from a singles party, and she ends up meeting Kim Hyun Jin, whom she marks as her Prince Charming. Being the determined young woman that she is, Hee Ji breaks into his hotel room the next day and steals his schedule. Seeing Hee Ji everywhere he goes, Hyun Jin gradually develops feelings for this cheerful girl who seems to match him so well. Things seem to go just fine until this carefully planned "fate" is finally revealed.