"The only person I trust is Mac, she'll keep the disc safe." said DS Marcus Farrow, just as we saw aforementioned Mac chucking said disc into the deep fat fryer and looking significantly mean.
Which meant that poor Farrow aka John Simm was in an even bigger fix than previously, particularly as he'd just nutted the one copper keeping an open mind.
Fortunately, this same copper DI Susan Reinhardt had the imagination to believe that Farrow just might not be the only bod on the force with a few secrets - and so the nut we'd seen inexorably tighten around Farrow's future began, albeit rather melodramatically, to be turned in the opposite direction.
All of this would have been distinctly average but for two things - Rosie Cavaliero surprising us with her natural, true performance as a befuddled but tireless policewoman just trying to get over her divorce and do a good job, and John Simm reminding us how the most predictable of scenes can be elevated by his subtle, deceptively small ways, and an ordinary show be carried on his big shoulders.