Season 1 of Sinister Beings premiered on May 3, 2021.

Hui Chun-sum (played by Ruco Chan) is an elite in the Organised Crime and Triad Bureau, but he aims to join the Special Duties Unit; while Sum Wai-lik (played by Ben Wong) is another elite in the Organised Crime and Triad Bureau.

However, the police force is attacked by terrorists, causing severe casualties. Chun-sam gives up his dream of joining the Special Duties Unit and stays in the Organised Crime and Triad Bureau. Chun-sam and Wai-lik work together to fight battles of wits with criminals to solve complex cases.

Season 2 of Sinister Beings premiered on April 1, 2024.

Officers Hui Chun-sum and Shum Wai-lik find out that Ngai Chi-lok, the culprit behind the Tiger Cull case, sent a secret message to the dark web before he was apprehended. They realize there is an evil conspiracy hidden behind Chi-lok.