This man just could not stop getting extorted, which is not ideal for anyone, but is especially unpleasant for the head of MI5. Spoilers ahead for “Scars,” the season-five finale of Slow Horses. Claude Whelan never stood a chance. I think he knows that now. I think he always knew it a little, probably, even as the rest of his brain tried to convince him he could manage a group of spies and analysts the same way one would manage a summer-internship program.