Jack is gone, and his classy personality and thoughtful attitude is sorely missed. The part of the show's time that was spent with Jack flows to obnoxious mentally defective Brian, and what a drag that is.
Brian goes to the retirement party of some old guy he blames for the death of the kid that was in his custody, and which got Brian retired / kicked off the Metropolitan Police. Brian assaults the old man, because he figures that will force a hearing and he will get to bring up the dirty laundry.
Brian got blamed for the death of a detained suspect because Brian was drunk and left the kid alone at the station. He wanted to get smoke a fag (cigarrette). He told some other guys to take care of the kid, and they ignored Brian, because nobody likes him. The kid is in the cell, and dies while drunken Brian is out smoking.
Brian gets the blame, and spends the next ten seasons griping and complaining that it was not his fault. But it was. He was drunk, he left the kid, and the kid died.
The fact that nobody took charge of the kid when some drunk shirked his job responsibilities is whose fault? Whose fault is it that drunken Brian has no friends that want to do him a favor?
In Brian's sick brain he wants justice for himself, and in his imagination he is doing it for the dead kid. After a confrontation at the hearing, his nemesis, Embleton admits he let the kid die by not watching him.
Why would he do that? The hearing was over, and Embleton had outsmarted Brian, so why would he make a terrible admission against himself? Of course Brian has taped the confession, and gives the tape to the kid's Mother, so presumably she can sue the Police Department.
Brian subsequently is suspended, and he goes on his psychotic way traveling to Gibraltar to "help" the other two guys that are investigating a murder. Brian marches to his own drum, disrespects Sandra, and their boss, and everyone else. He is mentally disturbed and out of control.
It is too bad that in season 10 they decided to write Brian as a really sick, narcissistic, dangerously obsessed character. His last few episodes are disturbing, and they are also a boring waste of time. I never cared about why Brian got retired, and the trip down the rabbithole of Brian's sick brain is unpleasant and unwanted.