In "The Shakespeare Code," Martha Jones gets to do something most people would want to do if given the chance to time travel with the Doctor: to visit an era that is well-known enough to feel familiar, but riddled with unanswered questions and untold stories.

Speaking of which, it is also partly a love story to the craft of writing, with subtle references to J.K. Rowling, Dylan Thomas and the various works of Shakespeare, and words playing an active part in dealing with a very real alien threat.

Best of all, the shadowy, unknowable figure of William Shakespeare is given thrilling form as a kind of Elizabethan movie star, slightly drunk on his own talent but unmistakably brilliant nonetheless.

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.)

The story of "The Shakespeare Code" is really the story of writer Gareth Roberts. A long-time Whovian, Gareth had written Doctor Who novels, games, audio plays, comic strips and the short TARDISodes that accompanied each story in Season Two. When he was finally asked to submit a script, Russell T Davies stipulated it should be about Shakespeare. This was already something of a specialist subject for Gareth. He'd already written the Bard into a Ninth Doctor comic strip called "A Groatsworth Of Wit" for Doctor Who Magazine in 2005, and written The Plotters, a novel in which the First Doctor takes Ian and Barbara to visit the Globe Theatre in 1605 and ends up enmeshed in Guy Fawkes' Gunpowder Plot. Gareth suggested a supernatural mystery based around the lost manuscript of Love's Labour's Won, a play referred to by contemporary accounts, but missing from Shakespeare's First Folio.

Gareth also considered which of Shakespeare's supernatural beings he should use in his story and whittled his wish list down to the three witches from Macbeth or the fairies in A Midsummer Night's Dream. Having chosen the former, he first named them Karyonites, then settled on the more vulture-like Carrionites, picking the name Lilith as being suitably ancient, derived from early Mesopotamian and Jewish mythology. Also, his first idea was that Bloodtide and Doomfinger would be her sisters, rather than her mothers.

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

The Doctor claims that Martha is from Freedonia, which is both the fictional country from the 1933 Marx Brothers' comedy movie Duck Soup and the name of an actual planet in the Fifth Doctor novel "Warmonger," written by Doctor Who stalwart Terrance Dicks.

Original titles for the story include the slightly too on-the-nose "Love's Labour's Won" and the even more descriptive "Theatre of Death." In the end "The Shakespeare Code" was chosen largely as a parody of Dan Brown's book "The Da Vinci Code."

When recording the audio commentary for this episode, Christina Cole, who plays Lilith, revealed that she had taken her pointy teeth home with her.

https://www.youtube.com/watch?v=3UcTdsgrhTs

Some of Gareth Roberts's fictional characters were given the names of real people—such as Wiggins (named after Professor Martin Wiggins, a big Whovian and Shakespeare expert) and Dolly Bailey (named after Big Finish writer David Bailey). They sit neatly alongside the real people who had existed in Shakespeare's time. There are the actors Dick Burbage and William Kempe and the genuine architect of The Globe, Peter Street (credited as Streete). There was also, at one stage, a plan to bring in Susanna, Shakespeare's daughter, as a character.

Doctor Who is the first television drama to have been granted permission to shoot inside The Globe Theatre in London, although they were only allowed to film at night, which required a few script amendments. There was a dramatic moment when it looks as if the filming would be cancelled thanks to contract issues, which would have required a complete redraft to place the action somewhere suitable, like the blasted heath on which Macbeth and Banquo first met the three witches in Macbeth.

https://www.youtube.com/watch?v=jgXKFwNw0oU

One scene that didn't make the cut was a long and involved sword fight between the Doctor and Lilith onstage at The Globe. It was cut for practical reasons, and not because of any apt well-known sayings about the pen and its relative mightiness to sharpened weapons of hand-to-hand combat.

When the Doctor, noting that Shakespeare appears to be just as keen on him as he is on Martha, mutters "57 academics just punched the air," it's a nod to the theory, hotly debated by Shakespearian scholars, that a good deal of his sonnets were inspired by—or written to—a man.

There is some confusion as to whether the Doctor has met Shakespeare before. Certainly the Fourth Doctor claimed to have known him well (in "City of Death"), noting that he was very quiet as a boy, and reassuring the young Bard with the words, "There's no point in talking if you've got nothing to say." He also said he had helped Shakespeare write down his first draft of Hamlet as the Bard had sprained his wrist writing sonnets. Furthermore, he offered some literary criticism, saying Hamlet was "Wonderful stuff. 'To be or not to be, that's the question. Whether tis nobler in the mind to suffer the slings and arrows of outrageous fortune or to take arms against a sea of troubles and...' Take arms against a sea of troubles? That's a mixed—I told him that was a mixed metaphor and he would insist!"

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