No sooner has the TARDIS brought the Doctor and Martha to New York City in the early days of the Great Depression than the travellers learn of a rash of disappearances amongst a burgeoning “Hooverville” transient community. With the help of Solomon, the Hooverville's unofficial mayor, the Doctor discovers a race of genetically-engineered Pig Men living in the sewers. Their masters are none other than the dreaded Daleks, who have perverted the construction of the Empire State Building in order to spearhead the next stage in their race's evolution.

Having set Dalek stories in the future and in the present during the first two years of the revived Doctor Who series, executive producer Russell T Davies thought that it was time to have the monsters appear in the Earth's past. Davies felt that this had been very successful when previously attempted -- most notably in 1967's The Evil Of The Daleks. This time, Davies envisioned a two-episode adventure set in Depression-era New York City (a setting chosen, in part, because Davies thought that the Cardiff docks could be made to look like their Gotham equivalents). He wanted to play up the Daleks' genetically-engineered nature, which he imagined would make them skilled in the discipline, and in turn inspired their Pig Men servitors.

To write the new Dalek story, Davies originally approached Steven Moffat, who had most recently scribed The Girl In The Fireplace for the previous season. Moffat was too busy to tackle the two-part epic, however -- he would instead write Blink for later in the year -- so Davies instead offered the job to Doctor Who script editor Helen Raynor. Davies had been very pleased with Ghost Machine, a Torchwood episode penned by Raynor, and felt that she was ready to write for Doctor Who itself. Raynor was offered the Dalek adventure around March 2006; consequently, her script-editing duties were reduced to give her time to write her screenplay. Raynor drew inspiration from the Universal Pictures stable of monster movies (such as 1931's Frankenstein), which were at their zenith during the Great Depression.

Reflecting the major plot points of the adventure, Raynor's scripts came to be called Daleks In Manhattan and Evolution Of The Daleks. Early on, Raynor set much of the action around the speakeasies which proliferated during Prohibition, including having Laszlo involved with the mob. However, Davies wanted to avoid the jazz music which would be predominant in such an environment, and so Raynor came up with the Broadway and Hooverville settings instead.

At one point, a major set piece saw Tallulah discover a cage full of the remnants of the Daleks' failed genetic experiments, but this was dropped due to expense. Another significant change was that Laszlo originally perished: Davies asked Raynor to alter this, as he felt the development was too depressing for the Doctor Who ethos. Mr Diagoras, meanwhile, was named for the fifth century BC Greek poet, Diagoras the Atheist, while Tallulah was an homage to the singer played by Jodie Foster in the 1976 children's musical Bugsy Malone.

The Dalek story was designated Block Four of the production schedule for the 2007 Doctor Who season. Its director was James Strong, who had helmed The Impossible Planet / The Satan Pit the year before; in the interm, he had also handled Cyberwoman and They Keep Killing Suzie for Torchwood. Strong was eager to make his realisation of 1930 New York City as believable as possible, and on August 30th learned that behind-the-scenes programme Doctor Who Confidential was planning to travel to the Big Apple with Raynor for an on-location interview segment. Strong suggested to Doctor Who producer Phil Collinson that a skeleton film crew could join them to take footage for Daleks In Manhattan / Evolution Of The Daleks; Collinson consented to this request on September 18th. Consequently, Strong spent October 13th to 15th at locations around New York City (including the Empire State Building, the Statue of Liberty, the Majestic Theatre and a bar called 230 Fifth on Fifth Avenue) taking plate shots and establishing shots.

Returning to Wales, Strong and his team then spent a week from October 23rd to 30th (with the exception of the 29th) at Upper Boat Studios, covering material in the Empire State Building, the sewer tunnels and the TARDIS console room. From October 31st to November 7th, the old NEG glass site at Trident Park in Cardiff Bay served as the transgenic laboratory. During the first day of filming there, it was discovered at the last minute that no hands had been ordered for Eric Loren's costume as the hybrid Sec, and so the actor was given a pair of black gloves to wear for the scenes in which Diagoras is absorbed by Sec. Subsequently, however, it was realised that the panic was all for naught: the hands had been fabricated after all. More sewer scenes were then captured at Upper Boat on November 8th.

Raynor had originally envisioned the TARDIS materialising on the roof of a Broadway theatre, but had amended this to the base of the Statue of Liberty. Since the budget did not permit David Tennant and Freema Agyeman to accompany Strong to New York City, this material was actually filmed at the Cogan Leisure Centre in Penarth, on November 9th. The same day, recording of the Hooverville sequences began in Cardiff's Bute Park; this continued until November 14th, omitting only the 12th. The Laurenzi theatre was really the Parc & Dare Theatre in Treorchy, where shooting took place from the 15th to the 17th. During this time, Tennant was combatting issues with his voice.

The backstage areas of the Laurenzi were actually parts of Headlands School in Penarth, with recording there spanning November 20th to 22nd. Part of the latter day, as well as the 23rd, were spent at the Cardiff Heliport, where the mast atop the Empire State Building had been constructed; shots of the Daleks hovering above Central Park were also captured there. Footage of a Hooverville guard was taken at Treberfydd House in Brecon on December 5th. Production then wrapped up with a variety of inserts shot at Upper Boat on the 8th.

Amongst the edits to Daleks In Manhattan / Evolution Of The Daleks was a Central Park sequence excised because it had been shot too late in the day, and so the light was insufficient. This involved the return of the Doctor, Martha and Frank to the Hooverville with Tallulah in tow, and saw the Doctor admit to Tallulah that he'd be unable to reverse Laszlo's transformation. Also excised was the opening TARDIS scene, in which Martha convinces the Doctor to take her on one last trip through time; this matched up with the opening moments of the next story to be broadcast, The Lazarus Experiment, in which the Doctor finally brings Martha home.

• Outpost Gallifrey: New Doctor Who Series News Page, edited by Shaun Lyon.
• Doctor Who Magazine Special Edition #17, 22nd November 2007, “Episodes 4 & 5: Daleks In Manhattan / Evolution Of The Daleks” by Andrew Pixley, Panini Publishing Ltd.