I must say, my disappointment in the finale wasn't because TLR didn't kill one of the main characters, or because Catherine didn't kill TLR.
There were just too many points that seemed a little too neat or far fetched. Alison just happening to have pills in her flat where Catherine slept that were supplied by Faisal, TLR breaking in a terraced row of houses in broad daylight (you can bet your arse I'd be glued to my window if I was Catherine's neighbour), never mind there not being a police car outside watching the house, Catherine not radioing through immediately when she saw the broken window, Catherine entering by herself, TLR being stabbed and half strangled yet manages to find the only rock in a field of grass to bludgeon his attacker with...
Ugh. No way claiming I could have written it better, mind, the acting was brilliant too.