"The Angels Take Manhattan" is a tough watch for fans of the close-knit TARDIS family group that revolves around Amy Pond, her husband Rory, their daughter River Song and her husband (to be), the Doctor. Amy and Rory have been slowly reasserting their independence from their time-traveling buddy, but with the Doctor having had the ultimate seal of approval from Rory's dad, they felt empowered to head out for a last jaunt or two.

Unfortunately, as far as their association with the Doctor is concerned, this story is where their luck—and Rory's incredible ability to die and come back to life again—has finally run dry.

Here are a few things to keep an eye out for, the next time you watch:

(The episode is available on iTunes and Amazon.)

Although it might seem as though the germ of the story would have come from the Statue of Liberty being a potential Weeping Angel—something Steven Moffat said fans had been suggesting to him ever since they first appeared in "Blink"—the original plan was that Amy and Rory would be separated from the Doctor by the Daleks. During a holiday in New York, Steven realized he wanted them to make their last stand in the city, but acknowledged that the Tenth Doctor had already covered this ("Daleks In Manhattan" / "Evolution Of The Daleks"), and opted to bring back the Angels instead.

The Doctor is seen checking his hair in a brass plaque, which reads "Type FD 12 MK V11 Rolls Royce Motors Crewe England", leaving spaces for serial numbers and even a NATO stock number.

This has caused a flurry of online activity, as fans try to work out the significance of the information on the plaque. The FD12 was a type of engine made by a Cheshire company called Fodens, made for marine use. According to one former employee, the engine had an aluminum casing, which made it ideal for minesweepers trying to avoid magnetic mines. Rolls Royce are thought to have purchased the design from Fodens.

There were also plans to have multiple Rorys and multiple Sam Garners in various different rooms at Winter Quay, and for the TARDIS to be knocked off course while trying to land in New York, and turning up in a Viking village.

Also, the ancient vase on which the Doctor enscribed the word "yowsah!" was originally intented to a puzzle box in the shape of the TARDIS. River was to have put her vortex manipulator inside it while in Grayle's office, then the Doctor would locate the puzzle box in a futuristic museum and use the device to travel back to Grayle's house.

Meanwhile, Grayle was to have been transported back to ancient China, to the very same workshop in which the puzzle box had originally been made. This was then changed to the idea that he would end up serving as a slave during the Renaissance, a fact that would only emerge when his face appeared on one of his antique paintings. Ultimately all of these ideas were shelved during production as they muddied the clarity of the story.

In the scenes at the beginning where the Doctor is reading his book, Amy is seen looking through The New York Record, a fictitious newspaper that previously made an appearance in "Daleks in Manhattan."

You'd expect to find the odd nod to Sherlock Holmes in a Steven Moffat script, and if you look at the first chapter of Melody’s book, it is called "The Dying Detective." This is also the title of a short story written by Sir Arthur Conan Doyle, part of the Sherlock Holmes collection entitled His Last Bow. And it can hardly be coincidental that the TARDIS lands in China in the year 221 BC, given that Sherlock's address is famously 221B Baker Street.

The idea for the Angel cherubs came from Bethesda Fountain in Central Park. Emma Stebbins, who designed it, placed an angel in the center—known as the Angel of the Waters—encircled by four cherubs who represent peace, health, purity and temperence. A scouting trip for shooting locations brought the fountain to Steven Moffat's attention, and he seized upon the cherubs to give the Angels a new twist.

In the scene at the end where the Doctor is reading the page with Amy's afterword in Central Park, Matt Smith had Karen Gillan reciting the lines to him just off camera, to help him get into the right frame of mind.

https://www.youtube.com/watch?v=TxrGUB5X-7Y

If you look at the credits at the end of the episode, you'll see the name Zac Fox appear, appearing as the unnamed Photoshoot PA. There is no one that matches this description in this story, but there is in "Asylum of the Daleks," in which Amy Pond is a model. Zac's credit did not appear at the end of that episode, so it was added to this one instead.

NEXT: "The Snowmen"

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