One sleepless night. One message to a stranger. One promise to keep living. Late one night, Heeseung stumbles across a post from a lonely girl in an online chatroom who feels like she has no place in the world. Unable to ignore her words, he reaches out. What starts as a simple message turns into nightly conversations that become the most important part of both their lives. But when the girl he's been trying to save turns out to be much closer to him than he ever expected, everything becomes more complicated.