Seven First Kisses - Season 1 Episode 4 : Till the End of the World 2017

While walking is a dark alleyway, Soo Jin is pulled by Ji Chang Wook, who is looking for the flash memory. He apologizes for getting her involved, but suddenly, a gun is raised to his head by a gang member, who claims that Chang Wook is a traitor and is actually a secret agent. Soo Jin is shocked to hear that she is also a secret agent. When the gang members attack them, Soo Jin helps Chang Wook and they escape to the safe house. There, Soo Jin treats Chang Wook's gunshot wound and asks him why he is doing this job. He tells her that it is his duty to protect and that he was her team leader at the agency back then. He also tells her that he fired her because he has feelings for her. He tries to leave but she follows him and asks him not to, and before he kisses her, she is back in time. (Source: MyDramaList)