Brash, arrogant Park Mu-yeol (Lee Dong-wook) is the star player of the pro baseball team Red Dreamers, renowned for both his skill and his bad temper. Stubborn bodyguard-by-trade Yoo Eun-jae (Lee Si-young) hates him; she's a lifelong fan of the Blue Seagulls, the Red Dreamers' rival team. The two mortal enemies are suddenly thrown together by fate. A chance meeting during a drunken night of karaoke leads to a scuffle, which former judo athlete Eun-jae easily wins, flipping Mu-yeol on his back. The fight was captured on video however and soon erupts into a huge scandal, with Mu-yeol's reputation and Eun-jae's career as a bodyguard at stake. To fix things, their respective employers agree to assign Eun-jae to act as Mu-yeol's bodyguard. The mismatched pair are now around each other round the clock, and in the midst of constant battling and working to find each other's weak spots, they find out more about each other than they realized.