But that doesn't mean they're always on the defensive. "An undercover officer has to know when to wait and when to move," Zhang said. "Sometimes the other side takes the lead; sometimes, we do."

While films and TV shows often portray undercover officers as lone wolves, Zhang stressed that real-life operations are a team effort.

"No mission is carried out by just one person," he said. "Behind every successful operation is a dedicated team, carefully planning everything — from the roles we play to the smallest details of how we act and speak."

And when danger strikes, it's his team that gives him courage. "Even when I'm alone in a closed room with suspects, I'm not afraid," Zhang said. "Because I know my team is right outside, ready with backup plans."

Behind the scenes

Life as an undercover officer comes with personal sacrifices. Zhang missed many family milestones — such as the birth of his second child — and appears in few family photos. Still, he believes the results are worth it.

Thanks to intensified law enforcement efforts and government support, he said, traditional drug trafficking routes through border areas like Dehong in Yunnan province have seen a marked decline.