One reason why Peter Capaldis portrayal of the Doctor is so powerful is his ability to swing from fun and games to bitter rage to glacial anger. The grief and tension between the Doctor and Jenna Colemans Clara is raw and moving as she prepares to face her death. Theres been an underlying sense of impending loss in the Doctors interactions with Clara the last few episodes and one has the feeling that he sensed this point coming and knew he could do nothing about it. He lashes out at Ashildr without hesitation making sure she knows her actions will have consequences. Despite Claras admonishment the Doctor at the end of this episode is a dangerously unstable one. This is a story that doesnt give you time to mourn but leaves you completely vested in what is to come. A Doctor reeling from grief and guilt and teetering on the edge of vengeance is a thematic concept rife with opportunity. Lets hope the Doctor never loses his edge and stays well away from melodrama as we explore what happens next.