Protégé is everything you want to know about drugs, but never knew. The film tells of a well-intentioned narcotics agent, Nick (Daniel Wu) deep undercover in the heart of Hong Kong's lucrative heroin trade. He is forced to deal with the hypocrisy and despair in a life of drugs and crime, as he plays protégé to one of the key players of the game, "Banker" (Andy Lau). In the eight years he has been infiltrating the heroin industry Nick has amassed enough evidence to indict Banker, but has just received orders to remain undercover in an attempt to expose the identity of the man behind Banker in order to bring down the entire organisation. However as Nick becomes more embroiled with Banker's craft and is increasingly entrusted with his confidences, he finds himself corrupted by the easy money and new found power.

Unable to separate himself from his undercover persona, he immerses himself into his role as a drug trafficker. Nick meets Jane (Zhang Jing Chu), a single mother living in poverty who has fallen prey to the dangerous narcotics that has also claimed her estranged husband (Louis Koo). Her brief affair with Nick, gives her a new hope for life, an escape from the past, but the re-emergence of her husband brings with it dire consequences.

In the seedy underbelly of heroin culture, where every redemption comes at a price and the borders of justice, loyalties and truth are permeable; Nick will have to grapple with some dangerous choices and may find himself flirting with more than the devil.