Almost a decade after directing patriotic blockbusters in Chinese mainland, renowned director Dante Lam has returned to the most familiar territory by helming a Hong Kong crime action thriller.

Bursting Point, Lam's first such title since his 2014 film That Demon Within, was released domestically on Dec 8.

Starring Hong Kong stars William Chan, Nick Cheung, and Isabella Leong, the movie follows an undercover police officer who becomes lost after being assigned to infiltrate a drug-trafficking gang. Walking a tightrope between good and evil, the protagonist not only has to deal with the criminals' suspicions and tests but also endure the misunderstanding and mistrust of his fellow police officers.

"I threw all the energy that had been accumulated over the past seven years into this movie, smashing everything could be smashed and overthrowing all (stereotypes) that could be overthrown," said Lam during a recent promotional event in Beijing.

Chan, who plays the undercover police officer, said that he has conducted extensive research to read a lot of stories about anti-narcotic police officers, discovering that some undercover agents have to endure a lot of sacrifices, such as losing significant weight or even being forced to consume drugs to gain the trust of traffickers.

"In real-life cases, what police officers experience is far more violent, bloodier, and more brutal than what is depicted in movies. I hope this film will prompt the audience to recognize the hardships and greatness of undercover police officers," said Chan.