The White Storm 3: Heaven or Hell

In the Hong Kong drug-dealing scene, drug lord Hong So Chai, subordinate Cheung Kin Hang, and new member Au Chi Yuen are like brothers. So when Hong So Chai's business starts getting investigated by the police, they flee to the Golden Triangle (where Laos, Thailand, and Myanmar meet) to plan and recover. However, they discover that there is an undercover agent amongst them. Are they a friend or foe?
(Source: Chinese = Douban || Translation = MDL)