Like the previous episode, this one didn't have me rolling my eyes about the improbability of the culprit carrying out the murder successfully. The means were simple enough to explain, and the motive lined up nicely with the psychology of the murderer as it's been presented to us. Once I realised the solution to the "Otis Falconer" mystery, everything clicked into place logically. (I probably vaguely remembered it from my first watch, but the point is that the who, how, and why were all perfectly plausible.)
Once again, my only complaint is that they categorically refuse to present their evidence BEFORE affecting the arrest. I mean, DI Mooney even mentions that he's sure they will find DNA evidence to corroborate their theory - why not just have them find said evidence first and then use it to refute the usual "this is absurd" half-denial from the murderer? Now that I've noticed this trend I can't unsee it...