A story where ten people get the chance to go back in time by one year, but unexpectedly mysterious situations start to arise when their fates are changed and twisted in the process.

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 cold-blooded hostage taker, Tae-gu, whose demeanors are difficult to interpret. Against the 21-hour deadline Tae-gu has set, Chae-yoon tirelessly tries to crack the unusually calm perp over multiple video-calls. Eventually, the shocking truth begins to unveil.

Life turns on a dime for a thriving prosecutor after meeting his new perky intern, who becomes a prime murder suspect soon after joining his office.

A police detective from 1986 travels in time to the present to save his daughter.