Seok-i (played by Kang Pil-suk) is a Chinese man who used to live in South Korea, where he married Eun-im (played by Kim Sae-byeok). He briefly returns to find out what happened to her after receiving a mysterious letter. Seok-i has to ask old friends to get any clue of what happened to Eun-im, and progress is limited. Much like Seok-i himself, Eun-im simply drifted away from the world she knew, since there wasn't anything to tie her down.
Tone of "Another Night" is quite poetic. That is a warning as much as it is an endorsement, because poetry can be pretty boring. Poetry has very little actual content, so most of the enjoyment of it is just about carefully reflecting over whatever small meaning you can find. Likewise, "Another Night" eschews plot or dialog, instead simply focusing on its bleak world with lonely characters who barely have any connection to the places they inhabit day in and day out.