Whether it was the moment DS Steve Arnott was left for dead and flung down the stairs (‘Noooooo!’), or the bit when forensics expert Tim Ifield lunged at DCI Roz Huntley with a chainsaw (‘Whaaaat?!’), the fourth series of the hit BBC drama has certainly not scrimped on shocks. And with the electrifying finale now fast looming, a little more collective jaw-dropping is definitely on the cards.