List of Gun Metal Grey episodes

Fifteen years ago, CID sergeant Shek Tung-sing (nicknamed "Stone") was sentenced to a lifelong jail term after he was accused of murdering a defendant lawyer and his wife at their home. At the time, Stone's on-and-off good friend Mai On-ting (nicknamed "Mad") was the only witness of the murder. Fifteen years later, Stone discovers a piece of evidence that is strong enough to prove his innocence after reading a magazine article written by Kim Hui. He is released from prison and resumes working as a CID sergeant.

Stone is sent to work in Special Crime Unit Team A, which is supervised by Mad, now a Senior Inspector. Stone suspects Mad to be one of the few suspects that is responsible for framing him.

Team A discovers a body of a young woman (Shum Po-yee) inside a kitchen stove that is enclosed with cement. They suspect that her husband (Chan Tik-hak), who is the first to discover her body, is the killer. They bring him in for questioning, but he is quickly released due to the lack of evidence. A few nights later, the team discovers the husband hanged at his apartment and concludes that his suicide was actually a murder. After further investigation, they find that Shum's "cousin" was actually a past boyfriend who killed the couple in a fit of rage.

• Based on the "Kitchen stove murder case" (灶底藏屍案) in 1975.