After the Frankenstein-style body horror of the Daleks in New York, "The Lazarus Experiment" takes a different horror trope—that of the Promethean scientist who plays with fire—throwing in a few gothic touches like a cathedral and some severe familial disquiet.

It is also, as we shall see, the story in which Mark Gatiss takes on a unique role within the history of Doctor Who.

Here are a few things that you should keep an eye out for, the next time you watch.

(The episode is available on iTunes and Amazon.)

Stephen Greenhorn, who wrote the episode, had discussed with Russell T Davies the idea of working on a mad scientist story, influenced by The Fly and Marvel comic creations such as Doctor Octopus and the Green Goblin, both of which were influenced in turn by Robert Louis Stevenson's The Strange Case Of Dr Jekyll And Mr Hyde.

However, Stephen had to rethink his initial suggestion that their mad professor should be working on a synthetic skin that made its wearer invincible, as there were worries that the film Spider-Man 3 might have a similar plot line concerning the alien parasite Venom. As it turned out, the movie's Venom worked differently from Stephen's idea, but by then he'd had a better idea...

Having decided that his scientist would unlock the secret of eternal youth, Stephen first elected to call him Professor Anger. Then he realized he could call him Lazarus, after the man saved from death in the Gospel According To John, and work in a wry aside for the Doctor ("Lazarus, back from the dead. Should've known, really."). So the script gained the title "The Madness Of Professor Lazarus."

https://www.youtube.com/watch?v=0EsZCRPb93Q

The final showdown was originally intended to take place in St Paul's Cathedral in London—since taken over by Missy and the Cybermen. However, arrangements to film there fell through, so the script was amended, moving over to Southwark Cathedral on the south side of the river Thames instead. Interiors for the cathedral were filmed in Wells, Somerset, which, incidentally, was also the location for the Edgar Wright movie Hot Fuzz.

The Doctor makes a joke about "reversing the polarity," claiming that he "must be a bit out of practice." This is the first reference in the reborn show to what has, over the years, been largely considered the Third Doctor's occasional catchphrase: "Reverse the polarity of the neutron flow." It's clearly on the Tenth Doctor's mind though, as there's the moment in "The Day of the Doctor" where he and the Eleventh Doctor both try and reverse the polarity of the time fissure at the same time, thereby "confusing the polarity."

https://www.youtube.com/watch?v=QDaCMhKPGys

Very few people have both written and acted in Doctor Who stories, and before Mark Gatiss, no one had done both at once. Having written stories such as "The Unquiet Dead" and "The Idiot's Lantern," and taken a major role here, it wasn't until his "Victory of the Daleks" that he achieved the double, making an appearance as the Spitfire pilot Danny Boy. He later turned up under heavy latex playing Gantok in "The Wedding of River Song," although for that part he was credited as Rondo Haxton.

Two other notable people have written for, and appeared in, Doctor Who; Victor Pemberton and Glyn Jones. Jones wrote one story, the First Doctor adventure "The Space Museum," and went on to appear as the astronaut Krans in the Fourth Doctor story "The Sontaran Experiment." Victor Pemberton deserves special mention, as he wrote (and also novelized) the Second Doctor story "Fury from the Deep," the first to feature the sonic screwdriver. The story was based on a radio serial he had previously written called The Slide, which starred Roger Delgado, who became the First Master. He had previously appeared in a non-speaking role as a scientist in "The Moonbase."

For his role as the revived Lazarus, Mark Gatiss wore his own wig, which he had previously used while playing the horrifically inept veterinarian Mr. Chinnery in The League of Gentlemen. Mr. Chinnery's gentle tone was based on Peter Davison (the Fifth Doctor), who had played the much less accident-prone vet Tristan Farnon in the BBC's All Creatures Great and Small.

https://www.youtube.com/watch?v=AJzL_wyMahU

In a deleted scene (which made it to the DVD release), the Doctor reveals that he not only took an active role in the drafting of the Declaration of Independence, but that he carries a copy of the first draft in his dinner jacket.

This episode is also notable for an appearance by British soap royalty: Thelma Barlow, who plays Lady Thaw, is best known to British TV viewers as Coronation Street's timid and prim Mavis Wilton, who worked in the newsagents and was therefore a horrified onlooker at the hub of social gossip.

https://www.youtube.com/watch?v=a9fmzsa7HIE

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