For those who haven't watched the first two series, there's no doubt about Dot - he's corrupt. We don't know what he's up to in this series yet though. It did look like he is starting to crack under the strain. We've never seen anything about his personal life before, so the scene in his flat with Kate was unnerving. And we've not seen him make mistakes before, like not ordering the 2nd post mortem and then telling a traceable lie about it. He's never been sloppy.
Every series has been the same - full of twists and turns. Brilliant.