On the morning of the Winter Solstice, Tang Yu's son disappeared out of thin air in the stairwell; Lin Yutong, a girl living alone next door, was violated while sleeping six months ago but did not report it to the police; Tenant Yan Wu hid his deceased father's body in a fish tank and wall to deceive his pension. Three seemingly unrelated clues eventually intersected in the dark wall passage of an old residential building, and the culprit turned out to be an acquaintance who nods and smiles every day. ‌‌‌