Banger. I have a soft spot for suspenseful horror things, ones that are more creepy than scary, and god this delivers on that front. The heartbeat sound got me every time, the possessed workers were unnerving, and the general dreary atmosphere and setting works perfectly for a story like this. And god that scene where Mrs. Harris walks into the sea is just impeccable. The vibes are great here, and more than enough to carry a six-episode serial.
It's a real shame this serial is part of season 5. I appreciate that it tries to do something new with Victoria, but she's still Victoria, and the whole "weaponized screams" thing almost feels like some sort of satire of the way 60s Who writes female companions. And while it's probably the most successful base-under-siege story for me, it loses its impact a little after a whole season of stories with the same format.
But still, I love this one. I said in my Daleks' Master Plan review that if I could resurrect a single episode it would be episode 12 of that serial – if I could resurrect a whole serial it would be this without a question. The animated reconstruction carries this well enough, and probably improves it in the case of the helicopter scene – but the whole time I was left wondering, wouldn't this story and this audio work better if it wasn't being delivered via clunky puppet animation?
(with all the love to the animation crews of course – I know just how hard they work on these things)