The man that Hastings visited in prison was the gang member that Arnott arrested in episode 2 (this series). During this visit I suspect he gave up Corbett.
I think Hastings gave up Corbett to the gang as his version of justice, because Arnott didn't arrest him when he had the chance (and he told him to), for the assault on his wife, the death of PC Bindra & the other police officers; and to make sure he doesn't kill anybody else.
By the time Hastings was on the laptop having the chat, Corbett was already exposed. Lise is definitely undercover but I don't think she's working for Hastings.
This is the first program I've watched in the last 18months including a storyline about women being trafficked. Not everyone watches all the other programs listed that have featured this issue. Women being used as sex slaves, housemaids, nannies etc are hidden away out of sight. The men in car washes are seen on a regular basis. I disagree that inclusion of this aspect reduces the quality of the program. Drugs, trafficking, guns, money laundering are the bread and butter for gangs of this size.
For the story arch the gang were having cash flow issues, couldn't sell their drugs or guns so trafficking is the next option, it makes sense.
I'm going to re-watch episode 3.