With much sweat and tears, widow Tong Shuk Fun (Louise Lee) single-handedly raises her two filial sons Chong Yau Ching (Ruco Chan) and Chong Yau Kit (Ron Ng) and sees them join Hong Kong’s elite police force ATF. The calm and intelligent Ching joins the force’s intelligence unit, while the athletic and passionate Kit joins the operations unit. Both earning the respect of their superior Shum Chi Ngo (Eddie Kwan), Shuk Fun believed that she could finally retire in peace.
However, under mysterious circumstances that came from a piece of intelligence, the two brothers suddenly change sides and become enemies. Ching discovers reliable information about a secret organization through journalist Yip Ting (Yoyo Mung), and he almost loses his life investigating it. Unable to reinstate himself back in the team, he convinces his girlfriend Chung Yat Ka (Aimee Chan), an intelligence analyst for ATF, to secretly obtain information from the force’s database to help with his investigation.
With details of the case leaking to the opposing organization, Kit believes that his brother is the mole. Ching however focuses his efforts on luring the real mole, abandoning all ethics in the process.