@Eugene's Lair posted:
DCC Andrea Wise is definitely a possibility, although again she may just be doing - however inadvertently - someone else's dirty work...
Chief Constable Osborne still seems the most likely and - AFAIK - remains the favourite. However we know from many years of watching Mercurio's work just how skilled he is in setting up red herrings. Consider PCC Rohan Sindwhani: I think the biggest surprise of Ep. 5 was discovering that he wasn't bent after all!