Joonho, a heart surgeon with a perfect smile, and Jisun, a free-spirited teacher-librarian, share a special night after a heart-fluttering date. The next day, they face each other at a police station with completely different memories. One of them is lying. With no evidence or witnesses, even the polygraph result defies expectations, and their mutual suspicion throws their lives into chaos. Questions about Joonho's late wife reveal that the case extends far beyond the two of them. As conflicting testimony and hidden relationships emerge, the truth grows murkier, and one lie sparks a dangerous game in which no one can be trusted.