SPOILER ALERT: the following article contains massive spoilers, including the ending. If you have not yet seen the movie, proceed at your own risk, or better, come back to this article later!
SPOILERS AHEAD
Knock Knock Plot Summary and Synopsis
That night, thief Lao Li (Fan Wei) entered a dilapidated residential building but witnessed a murder. The mysterious woman (Zhu Zhu) was bizarrely killed, and Lao Li is desperate to subdue the assassin Yan Zheng On.
Zhang Songwen and Ma Mingliang’s suddenly appear in the same room.
All three are completely ignoring each other’s personalities, and the ever-changing plot is about to reveal the truth.
Source: Wikipedia (CC BY-SA 3.0).