An ace police crisis negotiator, Chae-yoon, is called to the scene where her supervisor is taken hostage. Through the control room monitor, she is faced with the unusually calm, cold-blooded hostage taker, Tae-gu, whose reactions she is unable to interpret. As Chae-yoon’s endeavor to crack the mysterious hostage taker begins against the 21-hour deadline the perpetrator has set, the hidden truth between Chae-yoon and the perpetrator who specifically requested her as the negotiator unveils.