The story of two brothers, the younger one of whom has a rare disease which causes his body to age rapidly while his mind is still in a pre-teen state.
This is the story of a 7-year-old boy, Sang-woo, born and raised in the big city, and his mute grandmother, who has spent her whole life in a small rural village.
In the year 1999, a young woman leaves her quaint seaside house and returns to the city, leaving in the mailbox a card for the next owner, with instructions to forward any mail of hers to the new address. In the year 1997, a jaded young architect moves into the same house and finds the letter. His reply, which he slips into the mailbox, finds its way to her, beginning a parallel-time love story separated by a span of two years.
Two North Korean soldiers are killed in the border area between North and South Korea, prompting an investigation by a neutral body. The sergeant is the shooter, but the lead investigator, a Swiss-Korean woman, receives differing accounts from the two sides.