Ji-yeon, who works as a ticket collector at a tollgate, becomes alarmed when a mysterious black car pays its toll with a ticket stained with blood at the stroke of midnight. Her anxiety grows when her coworker, Jong-sook, recounts a story from 12 years ago about a prison transport vehicle that crashed, resulting in the deaths of all the prisoners on board, with some bodies mysteriously vanishing. Following this incident, a murder has occurred near the tollgate every leap year on February 29th. Strange occurrences begin to happen more frequently, often involving a double of Ji-yeon. When Jong-sook is murdered on one such February 29th, Ji-yeon, aided by two detectives, decides to investigate the situation herself.