The spin-off from a highly-successful TVB series of the same title, with only Charmaine Sheh and Hui Shiu Hung’s characters carried over from small to big screen, Jazz Boon’s Line Walker is a riotously enjoyable actioner that merges Infernal Affairs‘ undercover twists, some over-top action scenes from Benny Chan’s playbook, and goofy comedy out of Wong Jing’s less tasteless offerings (Wong is a producer here). The fictional CIB department of police is trying to dismantle a powerful crime organization, but all of its undercovers have been killed after their identities were leaked. Inspector Q (Francis Ng) and his colleague and girlfriend agent Ding (Charmaine Sheh) are contacted by a missing undercover agent known as Blackjack, who may or may not be Shiu (Louis Koo), the right hand man of a fast-rising figure of the crime organization, Blue (Nick Cheung), whose life he once saved.

Line Walker entertains flawlessly, embracing its more ridiculous plot turns with an aplomb that allows for some mildly poignant moments, which are mostly due to the impeccable bromantic chemistry between Koo and Cheung, and the endearingly ditzy and tender pas-de-deux between Ng and Sheh. The action is remarkably solid, especially a car chase in Rio and a protracted final fight where Koo and Cheung take on a formidably unstoppable Shi Yanneng. In the supporting cast, Hui Shiu Hung is excellent in a role far removed from his usual goofball persona, Clara Lee pops up as a scantily-clad assassin (who will complain?) and Zhang Huiwen (revealed in Zhang Yimou’s Coming Home) makes a strong impression in a limited role as a loyal and steely bodyguard who’s deadly with a telescopic baton. Character development is minimal and some comedic interludes jar a bit, but on the whole, Line Walker is a blast. Watch out for a blink-and-you’ll-miss-it appearance from the excellent (but all too rare on the big screen) Jade Leung, one of a few nice cameos peppered through the film.

Long Story Short: Carried by a charismatic cast, Line Walker is often ridiculous, frequently spectacular, and always entertaining. ***1/2