Artemis Entreri is now Barrabus the Grey. In which book did he become Barrabus the Grey? I read Transitions series already. Am I missing a series?
I'm assuming you're reading the Neverwinter Saga now. I'm not aware of a separate story that details how Artemis winds up in the situation he's found in there. I suspect that, as you work your way through those books, more details will become clear.