Lee Yoon-Sung (Lee Min-Ho) works at the Blue House for the National Communication Network Team. He graduated from M.I.T. in the U.S. and possesses elite skills as an I.T. engineer. At the Blue House, Yoon-Sung meets Kim Na-Na (Park Min-Young), who works as a bodyguard there. The two people fall for each other even though Yoon-Sung was warned not to fall in love. An elaborate plan for revenge is his ultimate mission ....