The story begins with Eun-joo moving out of a house by the sea called "Il Mare". As she is leaving, she leaves a Christmas card in the mailbox, asking the next resident to please forward her mail to her. Sung-hyun, an architectural student, receives her card, but is puzzled, since he is the first resident at "Il Mare" and the card is dated 2 years in the future. After a series of back and forth correspondences, Eun-joo and Sung-hyun realize they are living 2 years apart, Eun-joo in the year 1999 and Sung-hyun in the year 1997. After some testing, Eun-joo and Sung-hyun discover that the mailbox at "Il Mare" is enabling their communication and they can pass objects and living creatures through.