Kyungsoo is a cyborg, the scientists from M.A.M.A. Androids found a way to replace baterry energy with heart's energy, he's the first of his kind, more known as D.O., a cyborg that looks exactly like a human and no one knew about their existance.

      On a day, they brought him outside to examine his reactions with people, never would they know that a single cop/secret agent named Kim Jongin would blow all their plans up just by bumping into Kyungsoo.

      Will Kyungsoo be taught by Jongin how to be a human being, including love or will he get back to be a M.A.M.A's experiment ?