I know there's been a thread already but it didn't have spoiler in the title and I need to offload.
So - I loved it. And I've worked out that the comment at the end by Jackson - re the birthmark in the shape of Africa ringing a bell but he couldn't remember what - relates to Courtney; Tracey spots it on her arm early on, and then midway through when Jackson is thinking about Mitch, the South African who has a website of missing children, one of the children he lists has a birthmark in the shape of Africa.
So Courtney is one of Mitch's missing children - someone else is out there looking for her. I'm finding this bizarrely upsetting. And Tracey must realise this - she knew she wasn't Kelly's daughter - but carried on regardless. And who killed Kelly? Were there clues to that I missed?
And what was the point of Tillie? I realise she keeps the whole Lost Child thing going, but apart from that she was just an annoying diversion with a few tenuous links to the rest of the narrative - or am I missing something?