A young game developer Jung Se-joo based in Spain develops a groundbreaking AR game based on medieval battles in Alhambra and offers to sell the game to Yoo Jin-woo (Hyun Bin), CEO of an investment company that specializes in futuristic AR contact lens. Yoo Jin-woo went to meet the Se-Joo in Granada, Spain, but met with his sister Jung Hee-joo (Park Shin-hye) instead. Se-Joo was no where to be found.

While playing the game, mysterious incidents keep happening and Jin-woo found that the lines between Reality and AR starts to blur.