I think The Crimson Horror may actually be the best episode of the second half of this season. Like Hide, Gatiss' episode mixes sci-fi and 'horror' quite well. With the Doctor and Clara mysteriously absent for a relatively large portion of the episode, Vastra, Jenny and Strax are left to find out what has caused the deaths of so many. When the Doctor finally appears, it is not in a way you would expect. As the only one to survive (just barely) the crimson horror, Mrs Gillyflower's daughter, Ada decides to rescue him, keeping him chained up as her 'monster'. Jenny, sent undercover into Sweetville, finds the Doctor bright red and half-paralysed in a cell. Armed with the sonic screwdriver and what I'm assuming is the antidote to the poison, the Doctor is quickly back to normal and desperate to find Clara.
Of course, this is an issue for Jenny. Clara is dead, isn't she? The Ice-Lady pushed her off a cloud! Poor Jenny, despite vigorous questioning at every chance, never finds out how she is still alive. And here we go into the season's story arc - the mystery that is Clara Oswald. At the end of the episode, the kids she nannies have uncovered pictures of her from all across time. One of which is the Victorian-era Clara from The Snowmen. Though Clara knows that it is not her, it may have sparked something of the information the Doctor told her in Journey to the Centre of the TARDIS before he erased that timeline.
I really liked Ada, the blind and mutilated daughter of Mrs Gillyflower. As the imperfection in her mother's perfect world, Ada cannot help but save the Doctor, who at that point was an equally disfigured "monster". Caught crying when she finds him missing, her mother tells her she has no place in her "Eden" and asks her to stop "clawing and slobbering" at her feet. However, Ada still remains loyal to her. But, some encouragement from the Doctor, her monster who returned to her, she leads them to her mother. When she finds out Mrs Gillyflower had experimented with the crimson horror on her, she quickly turns against her.
It is here we find out about the crimson horror. In an odd reveal of Mrs Gillyflower's partner in crime 'Mr Sweet', she rips off part of her dress to show a red leech attached to her chest. Apparently, in return for a home(?), the leech, aka Mr Sweet, excreted the 'crimson horror' which Mrs Gillyflower planned to use to basically destroy humanity.
Strax was definitely a highlight. The out-of-place soldier has not lost his comedic value, always muttering about far simpler but much more violent ways to solve any problem. Strax seemed to be the centre of the jokes in this episode. The best one by far being Thomas Thomas. Strax, lost on his way to Sweetville and about to shoot his (fourth) horse for not knowing the way, was interrupted by a young Thomas, who did knew exactly where to go. The hilarious instructions were as follows:
Thomas: "Sweetville, sir?"
Strax: "Do you know it?"
Thomas: "Turn around when possible. Then, at the end of the road, turn right."
Thomas: "Bear left for a quarter of a mile and you have reached your destination."
*Thomas sits on the cart next to Strax.*
Strax: "Thank you. What is your name?"I think I'm going to be laughing at that for days.
Thomas: "Thomas, sir. Thomas Thomas."
One of the best parts of the episode was the retelling of how the Doctor and Clara ended up in Sweetville. It was done so brilliantly. A flashback, in the form of an old film - sepia, grainy and a bit bumpy, broke up the episode in such an awesome way. It looked fantastic, adding to the feel of Victorian England and quickly let us know what had gone on beforehand.
Overall, I really liked this episode. Though I don't know how much it adds to the overall story arc, it was still a great mix of action and comedy.