Evil was initially intended to be the last Dalek story on Doctor Who. Writer Terry Nation, the creator of the Daleks, was busily trying to sell the Daleks to American television at the time and it was intended to give them a big send-off from the series. However this was not to be his last encounter with them. In 1993, readers of DreamWatch Bulletin voted The Evil of the Daleks as the best ever Doctor Who story in a special poll for the series' thirtieth anniversary.
They wake up to find that they have been transported to 1866, and are in the house of Theodore Maxtible, Waterfield's partner. The two had been trying to invent a time machine using mirrors and static electricity, when the Daleks emerged from their time cabinet. The Daleks then took Waterfield's daughter Victoria hostage and forced Waterfield to travel a century forward in time to lure the Doctor into a trap by stealing the TARDIS. Waterfield is obviously fearful for his daughter's safety and his own, but Maxtible seems to be going along with the Daleks for his own reasons.
The Daleks threaten to destroy the TARDIS unless the Doctor helps them by conducting an experiment to isolate the "Human Factor", the unique qualities of human beings that have allowed them to consistently resist and defeat the Daleks. Once the Doctor has isolated the Human Factor, he will then implant it into three Daleks, which will then become the precursors of a race of "super" Daleks, with the best qualities of humans and Daleks. To that end, the Daleks want the Doctor to test Jamie by sending him to rescue Victoria, who is being kept in the house. The Doctor is strangely co-operative with the Daleks, manipulating Jamie into the rescue mission but not telling him of the nature of the test.
Jamie manages to rescue Victoria, but she is taken prisoner again and transported through the time cabinet. The Doctor, observing how Jamie accomplished the rescue, distills the Human Factor, but continues to harbour suspicions that there is more to the experiment than just this. Once the Human Factor is implanted in the three Daleks, they become completely human in personality and seem almost child-like, although the Doctor says their mentalities will mature quickly. This was the Doctor's intent all along, that the human factor would lead to "human" Daleks that would be friendly to humanity. He christens the three Alpha, Beta and Omega, but they soon return through the time cabinet to Skaro, the Daleks' home planet.
Meanwhile, Waterfield has discovered that Maxtible has betrayed them all to the Daleks, hoping that he will be able to learn the alchemical secret of transmuting base metals into gold. However, Maxtible, who has travelled to Skaro through the mirror cabinet, is discovering just how ruthless the Daleks are and how empty their promises can be; he is tortured for his failure to bring the Doctor to them. Jamie, Waterfield and the Doctor are locked out of the time cabinet, but manage to use the Daleks' own short-range time machine to make the journey to Skaro before a Dalek bomb destroys Maxtible's house.
The trio find their way into the Dalek city and are brought before the imposing Emperor Dalek, who reveals the true reason behind the experiments and the capture of the TARDIS. By isolating the human factor, the Doctor has succeeded in isolating the "Dalek Factor" as well. The Daleks will use the "Dalek Factor" — the qualities that make the Daleks mindless killing machines — to reconvert the "human" Daleks. In addition, the Emperor wants the Doctor to use the TARDIS to spread the Dalek Factor throughout human history, turning all humanity into Daleks. The Doctor knows that the Emperor realises that he would die before complying with this order, and so is concerned about why the Emperor seems so confident.
Maxtible is tricked into walking through an archway that infuses him with the Dalek Factor, mentally turning him into a Dalek. He hypnotises the Doctor and lures him through the arch as well, apparently converting him. However, the Doctor is feigning his conversion, and secretly plants a device on the arch while the Daleks hunt for the three "human" Daleks. As one still remains to be found, the Doctor suggests that all the Daleks be put through the conversion arch so that the "human" Dalek will once again be infused with the Dalek Factor.
As the first batch of Daleks go through the arch, the Doctor frees the others. The arch did not work on the Doctor because it was calibrated for humans, and he is not one. The Doctor has also substituted the Human Factor for the Dalek one on the arch so the Daleks that go through will become "human" and rebel against the Emperor. The Emperor calls out his Black Daleks as the rebellion spreads and the city falls into chaos. Waterfield throws himself in front of a Black Dalek blast meant for the Doctor. The Doctor promises that Victoria will be taken care of, and Waterfield dies content. The Emperor is attacked and exterminated by the "human" Daleks. While the Doctor and his companions escape, Maxtible rushes back into the exploding city, screaming of the everlasting glory of the Dalek race.
The Doctor tells Jamie that they will be taking Victoria along on their travels. Jamie, Victoria and the Doctor watch the Dalek city in flames from the top of a hill as the civil war continues. The Doctor pronounces this as the end of the Daleks — the final end.
Excluding Earth, the Doctor's journey to Skaro (via time cabinet) is the first time the Doctor returns to an alien planet visited in a previous story (although scenes on Skaro were featured in The Space Museum and The Chase). It was not until The Monster of Peladon that the TARDIS itself would revisit a world it previously landed on.
Episode seven of this serial is the first time that the Doctor admits to being other than human.
The story of the humanised Daleks was followed up on in the Doctor Who Magazine comic strip story Children of the Revolution (DWM #312-#317), featuring the Eighth Doctor and his companion Izzy. This contradicted an earlier comic strip (Bringer of Darkness, DWM Dalek Special), that took place after the events of "Evil". In the story, a group of marooned Daleks inform The Doctor that the rebel factions were destroyed and the Emperor again reigned supreme. Like all spin-off media, both strips canonicity in relation to the television series is unclear.
Another Dalek is "humanized" after assimilating Rose Tyler's DNA in the Ninth Doctor episode Dalek. Like the Daleks in "Evil", this Dalek begins experiencing emotions like fear and empathy, and subsequently questions the instinctive Dalek xenophobia.
Other versions of a Dalek Emperor would appear in Remembrance of the Daleks (1988) and The Parting of the Ways (2005). Executive producer Russell T. Davies would dub Dalek heads of state "Puppet Emperors" in the 2005 Doctor Who Annual.
Features guest appearances by Windsor Davies, Brigit Forsyth and Marius Goring. See also Celebrity appearances in Doctor Who.
In 2004, analysis of the repeated clip used in The Wheel in Space episode six revealed it to be from episode one rather than episode two, as had been long believed. This, however, only constitutes a few frames of recovered footage.
The discovery of a behind-the-scenes film, The Last Dalek, made by the special effects team as they worked on the story's conclusion, facilitated a recreation of the climactic battle scenes. This recreation, along with the entire film, have been made available in different forms on various Troughton releases. In addition, telesnaps exist for the entire story.
On youtube there is a reconstruction of episode one using telesnaps and surviving footage.
In 2006, the BBC and the Terry Nation estate licensed a stage version of the serial, adapted for the theatre by Nick Scovell with an orchestral score by Martin Johnson. It was performed at the New Theatre Royal, Portsmouth in October.