Minjoo moved to the house next to Chaewon's and since that day their lives were never the same. This is the story of how their fellings changed through time and they grew closer as friends and then lovers, one step at time.

At the night before their high school graduation Chaewon and Minjoo promised one thing: To marry each other if they were still single by the age of thirty. Eleven years went by, but none of them forgot about the promise.