Line Walker (Chinese: 使徒行者 literally "Apostle Walker") is a 2014 Hong Kong crime thriller drama produced by TVB, starring Michael Miu, Charmaine Sheh and Raymond Lam as the main leads, with Sharon Chan, Benz Hui, Elena Kong, Sammy Sum, Oscar Leung and Toby Leung in major supporting roles.

He is a righteous supervisor that will resort to unofficial tactics in order to restore the identities of his undercover subordinates who have gone missing and deemed by the police department to have strayed to the criminal side.

With clues left behind by Hong, Hoi finds undercover agent Ting Siu Ka (Charmaine Sheh) who fronts as an owner of a foot massage parlor, and assumes his role as her new handler.

Siu Ka previously clashed with Bao Seed and his partner Muk Sut when they went to her shop to collect a gambling debt but becomes friendly with them because she knows of their connection to a major triad organization.

Meanwhile, Kobe Lin Ho Kan (Sammy Sum), another undercover agent working for Hong, fronted as a crooked stock broker in order to go to prison and get close to triad boss Chum Foon Hei as the last assignment he received from Hong, but Foon Hei soon proved to be a cunning target.

Yan investigates Hoi because she suspects that he is a dirty cop with connections to the triads because of his fast raise in the police force and all the cases he is assigned to as the Chief inspector gets foiled.

Accidentally he discovers the abusive marital life of Yan's older sister Katie Mok Sin Ching (Elena Kong).

At first Yan dismisses Kobe's warning as an act of jealousy; however, she decides to investigate on her own and finds evidence to confirm Hoi's suspicions.

The series has received overwhelming critical acclaim since its release particularly for the suspenseful plot, buzz-generating episodes, performances by the casts, and direction.

The subtheme "Love Is Not Easy" (越難越愛), sung by Jinny Ng, won the first Most Popular Series Song at the TVB Anniversary Award.