Felix Wong as Shek Tung Sing / Stone Sir
Michael Miu as Mai On Ding / Mad Sir
Jessica Hsuan as Hui Man Him, Kim
Nancy Wu as Hui Man Sze
Vincent Wong as Carson Ko
Total Episodes: 30 episodes
Aired Dates: November 1 to December, 2010
Time Slot: Mondays to Fridays, 9.30pm
Channel: Astro Channel 921
Fifteen years ago, Shek Tung Sing, a just and upright police officer, was imprisoned for murder which he did not commit. Now, fifteen years later, he is released from prison and vowed to find out the truth. Unfortunately, after finding out who the real culprit was, Tung Sing is unable to bring him to justice due to the lack of evidence.
Tung Sing was furious and angry at the failed system of justice and supresses his anger within him. Due to this, each time he comes across a case which the law fails to carry out justice, Tung Sing takes matters into his own hands.
Tung Sing's sudden change in character and behaviour worries his best friend, Mai On Ding. It also puts their friendship to test. Tung Sing tries to prevent On Ding from further investigating into a case and in the process hurts On Ding's girlfriend, Hui Man Him.
As a result, On Ding and Tung Sing's relationship took a turn for the worse, and On Ding was determined to bring Tung Sing to face the law.
Gun Metal Grey is a story about a police officer's road to self-destruction as well as provides viewers with an insight into Hong Kong's most famours 10 unsolved crime cases.