Ming, now cleared of charges and assigned to the Internal Affairs division, uncovers a potential mole in the police department, Yeung, who has a mysterious connection to Shen, Sam's mainland link. Ming suspects Yeung is working for Sam and works to expose him, while also hiding his own ties to Sam. As Ming investigates Yan's final days with Dr. Lee, flashbacks reveal Yan's dealings with both Yeung and Shen. The tension escalates
