It's back to the Victoria Period in Mark Gatiss's second episode for Series 7, Part 2.

Yorkshire. 1893. As the number of deaths attributed to the mysterious "Crimson Horror" climbs, the ever-inquisitive Doctor and Clara find themselves prisoners of the charismatic Winifred Gillyflower's Sweetville, by all appearances, a rather unremarkable match factory—but for the fact that "no one who ever goes to live there ever seems to comes out."

Meanwhile, in London…

"Tell me, madam… do you know what an optigram is?"

"Huh! It's a silly superstition, sir. The belief that the eye can retain an image of the last thing that it sees."

Reaching into his breast pocket, Mr. Thursday produces evidence to the contrary—hoping to enlist the services of the Veiled Detective, Madam Vastra, in discovering the cause of his twin brother Edmund's suspected murder. Evidence that the Doctor has returned and was the last thing that Edmund saw before he died.

Of the Crimson Horror.

The game's afoot.

As Madam Vastra, Jenny, and Strax arrive in Yorkshire, it's agreed that Jenny, "the fittest and the most beautiful" of the three, will infiltrate Sweetville to locate the Doctor and, in so doing, very likely gain a step closer to solving Mr. Thursday's case. Strax has his doubts, but deep into the black heart of the curious place, Jenny discovers the Time Lord, locked up like a monster, afflicted by the Crimson Horror, but having survived—maybe, because he's not human.

With Jenny's help, the Doctor is able to revive himself. Keeping it short, he explains that he and Clara—"It's complicated"—arrived in Yorkshire days-weeks-don't-know-ago by accident; they were expecting the land in London. There'd been a scream. A body had been discovered floating in the canal. They'd met Edmund. The three had followed the body to the morgue, where he and Clara had learned about "The Crimson Horror." There, they'd also discovered an image of Mrs. Gillyflower in the dead girl's eyes. So, naturally, they'd come up with a plan to infiltrate Sweetville: "The Doctor and Mrs. Smith." But, once inside, they were surprised by Sweetvillains and exposed to the Crimson Horror. Clara, he thinks, survived her exposure—part of Mrs. Gillyflower's preservation process against some coming apocalypse—but, in his case, something went wrong, and "only Mr. Sweet knows why." Trapped in his own skin, he was befriended by Mrs. Gillyflower's blind daughter, Ada, who locked him away, safe from her mother, who would have seen him tossed into the canal with the rejects. He became Ada's secret. Her "special monster." At some point, Edmund, having gone looking for Clara and himself, the Doctor conjectures, "must have fallen into a vat of the pure venom—or was pushed," then stumbled upon the Doctor's cell, where he died. Hence, the last thing that he saw.

But, right now, it's Clara they've got to find.

They find her, free her from her glass prison, but are discovered by a group of Sweetvilliains before the Doctor can completely revive her. Jenny takes them on single-handedly. Strax shows up and starts shooting. Madam Vastra isn't far behind. As the smoke clears, Clara comes to. Brief introductions. Then Madam Vastra reveals that she suspects that the Crimson Horror is actually a derivative of her species' most deadly plague, most virulent enemy: the Repulsive Red Leach.

On balance, the Doctor prefers the "Crimson Horror:" "But what's the connection to Mrs. Gillyflower? 'Judgment will rain down on us all.'"

Clara has an answer: "A chimney that doesn't blow smoke."

Within that chimney, Mrs. Gillyflower and the parasitic symbiote Mr. Sweet have constructed a rocket to poison the air.

The Doctor comes up with another plan.

While Madam Vastra and Jenny see to the poison and Strax keeps watch outside, the Doctor, Clara, and Ada confront Mrs. Gillyflower and Mr. Sweet as they prepare to launch the rocket remotely. Furniture is tossed about. The remote control is destroyed. Mrs. Gillyflower and Mr. Sweet appear to have been thwarted. But Mrs. Gillyflower won't be stopped that easily: taking her daughter hostage—gun to her head—she escapes with Mr. Sweets.

The Doctor and Clara catch up to them, but not before Mrs. Gillyflower can launch the rocket manually. As it ascends, Madam Vastra and Jenny emerge from the shadows, revealing at the snap of the Doctor's fingers that the poison has been removed and the rocket has been rendered harmless.

"Very well then. If I can't take the world with me, you will have to do. Die you freaks! Die! Die!"

"Put down your weapon, human female," intervenes Strax, having apparently scaled the outside of the chimney and, even more surprisingly, actually getting her sex right.

She doesn't.

He puts her down.

As she lies dying, Mr. Sweets attempts to escape. This time it's Ada that intervenes, brutally bashing him to pieces with her cane.

Day saved.

Back at home, Clara is surprised to find a laptop open to pictures of herself—from 1983, 1974, and… 1892?

"That's not right."

"You're in Victorian London."

"No; I was in Victorian Yorkshire—"

It’s too late; the children have already figured it out.

"Time travel! That's so cool!"

"Can we have a go?"

Great Lines

Strax: "And how will she locate the Doctor?"

Madam Vastra: "To find him, she needs only ignore all 'KEEP OUT' signs, go through every locked door, and run towards any form of danger that presents itself."

Strax: "Business as usual then."

Madam Vastra: "Strax! You're over-excited. Have you been eating Ms. Jenny's sherbet fancies again?"

Doctor: "I'm the Doctor. You're nuts. And I'm going to stop you."

Doctor: "Mrs. Gillyflower, you have no idea what you are dealing with. In the wrong hands, that venom could wipe out all life on this planet."

Mrs. Gillyflower: "Do you know what these are? Ha, ha, ha. 'The wrong hands.'"

Jenny: "But, Doctor… that girl, Clara… you haven't explained?"

Doctor: "No… I haven't."

Doctor: "You're the boss."

Clara: "Am I?"

Doctor: "No. No!"

Wibbly-wobbly Timey-wimey… Stuff that You Might Have Missed

Mark Gatiss's previous episode, "Cold War," was set in 1983. This one's set in 1893. Same numbers. Different arrangement.

If the Crimson Horror seems familiar, it may be because of an Eighth Doctor story entitled The Dying Days and, coincidentally, involving the Ice Warriors (featured in Gatiss's previous story), who, in the novel, have engineered an airborne poison called the "Red Death." The Crimson Horror is also seemingly a play upon the "Red Death" of Edgar Allan Poe's "The Masque of the Red Death:" when the Doctor and Clara confront Mrs. Gillyflower in the organ room, she offers them "a glass of Amontillado," undoubtedly, a reference to another Poe short story, "The Cask of Amontillado."

The episode takes place the year following the events of "The Snowmen."

"I once spent a hell of a long time trying to get a gabby Australian to Heathrow Airport" is a reference to Tegan Jovanka, companion to the Fifth Doctor (and, very briefly, the Fourth Doctor before him) who accidentally entered the TARDIS believing that it was a police public call box after getting a flat (see "Logopolis").

Both of Madam Vastra's residences—in London and in Yorkshire—have (TARDIS?) blue doors.

Speaking of colors… Clara's signature color is all over the episode.

Thomas Thomas is the original TomTom.

When the Doctor and Clara discover Ada on their way to confront Mrs. Gillyflower and Mr. Sweet, Ada advises Clara, "You are fortunate indeed. It isn't good to be alone"—advice that forces us to revisit the lonliness that has characterized the Eleventh and previous Doctors—especially, in the new series, where he is the Last of the Time Lords.

The satiny detail work on Clara's dress resemble hearts.

In one of the shots inside the organ room, a wood carving of a bird, which may be a phoenix (note the long tail feathers), can be seen behind Mrs. Gillyflower.

Mrs. Gillyflower refers to what she and Mr. Sweet are planning as the "Great Work"—suggesting, perhaps, a connection to other great evils, such as the Great Intelligence.