Sun Woo is a son with a special emotional bond with his mother but has a secret he can't share. He was a field agent at the National Intelligence Service but is working for the intelligence analysis on North Korea after failing the operation. He tries to catch Hwang Ki Chul, who killed his partner. His mother, Hye Rim, was a spy in the past, but she currently keeps her identity hidden. She has kept it a secret from Sun Woo but when Ki Chul shows up, she becomes a spy once again to protect her son. And along the way, Sun Woo learns the identity of his mother. The mother and the son fight to protect their beloved family and Ki Chul's revenge begins.