The Bootstrap Paradox. As also seen in Blink and The Big Bang but never mind. ;)
The Fisher King - looks cool if a bit like a Warhammer 40000 version of a Vervoid, sounds cool (Peter Serafinowicz and Corey Taylor), and his role could have been any pseudo-mystical bad guy really. No particular link to the story the name comes from that I could see either.
Okay, Tivolians are now just creepy.
Aw no, not O’Donnell... Shortest-lived companion ever?
The sound dropping out for Cass’s POV is a nice use of her deafness, though it undercuts the not-making-a-big-deal-of-it it works. Not so sure about the Daredevil vibration effect, though.
The solution was planted cheekily as the solution to one of the problems last week (in the same room, no less) apart from the bit that, as noted at the top, wasn’t.
Favourite moment - Cass realising that just because Lunn hasn’t seen the writing doesn’t mean he’s safe and calling Clara on it.