Capaldi’s first three episodes were pretty good, but I don’t think anybody was blown away by them. “Listen” kicks off a run of seven really entertaining stories. This one is simply an absolute masterpiece. The Doctor hypothesizes that something unknown might exist, and so he decides to pick a fight with it. It’s a perfectly bonkers idea, and it’s done brilliantly.
I love how it doesn’t obey anything at all like conventional television narrative structure. It doesn’t have rising action or resolution or anything like what they teach you in screenwriting class. It’s like Steven Moffat just punched out some fic to amuse himself and told Douglas McKinnon to shoot it. Our son said it was weird, and then backtracked and clarified “I know that you asked me to stop just saying everything is weird, but seriously, that one really was weird.” And it is, weird and wonderful and scary and funny and perfect.