BBC News
By Steve Holden
**Warning: This article contains spoilers for season six of Line of Duty**
Who is H? Is Ted Hastings a bent copper? Where does Steve Arnott get his waistcoats from?
Line of Duty has once again thrown up as many questions as it's answered - but things do seem to be coming to a head with the series six finale.
Martin Compston, who plays DI Steve Arnott, says the cast and crew are "chuffed to bits" with the show's huge audience ratings.
"We're more popular than ever and seem to be getting in more and more fans the longer this goes on," he tells Radio 1 Newsbeat.