A mystery mini-series with a story that revolves around a promise that refuses to go away over time and characters who are faced with tough decisions to keep that promise. To keep their values, characters are at a critical juncture to act upon their promises. Lovers, played by Han Chae Young and Lee Byung Hun in this romantic mystery by Lee Jae Kyu tells a love story that transcends more than 100 years (1907-2010).

Kim Hyun Joon is an assassin who belongs to a top secret organization known as the "NSS" whereas T.O.P is an assassin who works in another secret organization located in the United States called "IRIS" and was ordered to kill Hyun Joon. Seung Hee is a psychological analyst who plays an important role in bring Hyun Joon into the "NSS." Jin Sa Woo is Hyun Joon's enemy and falls in love with Seung Hee as well.

As a kid, all Kim In Ha ever did was follow his uncle around and help him cheat in gambling. As a high school student, he hung out with his friends at the basement of a theater. As Kim In Ha gets to know Choi Jeong Won, a model student and also the son of a very rich family, In Ha tries to tempt him into doing mischevious deeds.

Young-jun, president of Young-Eum Music, fights the conspiracy of Sungchoon, president of rival company, Victory Records. But he ultimately dies while fighting. Sungchoon and his people cover up Young-jun's death as an accident. Young-jun's wife, Myungja, gives birth to their son, Sung-jae but due to Young-jun's sudden death, she falls into grief. Sungchoon has also been raising his children, Min-chul and Min-ji, alone after his wife's death. He proposes to Myungja and she accepts.In the meantime, at an orphanage, Yeon-soo and Sae-na, two orphans as close as sisters, are preparing for a birthday party for just the two of them. Coincidentally, the president of Victory Records, Sungchoon and his son, Sung-jae, happen to visit the orphanage.Time passes and … Yeon-soo works hard at making a living by teaching art and working at a restaurant. On the Christmas when Yeon-soo and Sae-na promised to meet, Yeon-soo is involved in an unexpected car accident and is unable to keep her promise. From then, they walk separate paths without learning of each other's whereabouts.