This episode totally hit the spot, I like the whole concept of a two parter shown 'after and before' as it were. I am a big fan of Toby Whitehouse's writing, he's given us some great Who episodes, but also BBC2 Spy thriller 'The Game.' I loved the prompt cards Clara had for the Doctor, Capaldi was truly back on top form, back to his matter of fact ways. I think this featured one of my all time favourite lines, 'whatever song I heard first thing in the morning I was stuck, 2 weeks of Mysterious girl by Peter Andre, I was begging for the brush of Death's Merciful hand,' genius!! Much more old school feel to this one, underwater base under siege a la Fury from the Deep or Warriors of the Deep, but the format has worked beautifully well in the past, and continued to work brilliantly here too. There was more atmosphere in this episode then you can shake a stick at, it was superbly lit, and Murray Gold's score was the best and most original one I'd heard for ages, loved it. It boasted some genuinely tense and scary moments. Plaudits for the story, it was a really interesting one, and also great to see deaf actress Sophie Stone too. Big fan of Arsher Ali, always great to see him, he's a terrific actor. The furniture enthusiast will notice the recent love for Vitra chairs, this week we had a cool Orange Eames chair, last week Skaro's sole chair was a Panton. (I need to get out more!) Loved it. 9/10