The drama stars Bobby Au-yeung as the famous historical forensic medical expert Song Ci ("Sung Chee" in Cantonese romanisation).

Set during the Southern Song Dynasty of Mid-Imperial China, Witness to a Prosecution tells a fictionalised account of Chee's modest beginnings and the events leading to the creation of his book Collected Cases of Injustice Rectified, the world's earliest documentation of forensic science.

For 30 years, nighttime keeper Song Ci (Bobby Au-yeung) was despised in To Yuen village due to his posthumous birth in a coffin, having only the sickly scholar Sit Dan (Michael Tse) and the coolie Cha Siu-chaan (Lo Mang) as his friends.

The village's newly appointed magistrate Sung Yik (Frankie Lam) finds the case suspicious and investigates.

With the help of the mysterious yet experienced coroner Ma Kwai (Lau Kong), Yik successfully revokes Ci and Sze's sentences.