We were left with the possibility that the son might prevent his mother from driving off and telling her that his dad was the murderer. Something he promised he wouldn't do. So, the biologicl dad goes down for a murder he didn't commit, the real culprit gets away Scott free though with his personal life in absolute tatters. Decent enough ending, imho. Not every murder is solved.
which bit didn't you understand? Kiri died by accident - she fell while running away from her adoptive dad and hit her head on the rock. I don't know why he wasn't honest about the accident but then it would have been over in two episodes.
I thought it was a very unsatisfactory ending. The son found out the father had killed Kiri but promised not to say anything, and the mother thought the son had done it so shipped him off to boarding school, and the real father goes to gaol for a murder he didn't commit. Quite distasteful if that's the right word.
The bit that puzzled me was that the woman detective definitely said to the biological father "you struck her with a rock and strangled her". So how does that tie in with the falling and hitting her head.
I sincerely hope they don't go and spoil it all by having a second series that has the real culprit discovered, thereby placating all those who like their Is dotted and Ts crossed.