First meet with Popstar, who asks you to beat up some of his customers and get the money they owe him.
You need to beat up some thugs before hacking a camera and heading back to the apartment to watch over a drug deal. You then need to correctly identify the supplier and get him arrested.
Another drug bust must be completed. Get in to the "chicken van". You use this to tail Popstar to the deal. Tailing him is pretty simple, just drive carefully. Spy on him and take a picture of the deal from cover. Take a second picture when the supplier reveals the drugs.
Follow Popstar to the docks. Fast talk the guard and get up to a nearby roof. Popstar shoots the supplier; you must photograph this. Call Teng and head back to the Undercover HQ. The police try and apprehend you, so you must escape them first.