With the creation of the hybrid Dalek-Human in the previous episode, the Doctor confronts the Cult of Skaro and helps Martha (Freema Agyeman) and Frank (Andrew Garfield) to escape. Dalek Sec (Eric Loren), now part human, begins to express human emotions for the first time. Dalek Caan and Dalek Jast (both voiced by Nicholas Briggs) have little confidence in him. Solomon (Hugh Quarshie) is killed when the Doctor and Martha return to Hooverville, but the Doctor is brought alive to the Dalek laboratory at the Empire State Building.
The Doctor learns that the Daleks are planning to combine their DNA with humans and make more hybrids. Since they cannot get a sufficient power source for this in 1930, they plan to use gamma radiation from a solar flare. The Doctor agrees to help when he realizes that the humans they have already seized are brain dead. He even offers to bring them to a whole new planet in the TARDIS. Dalek Sec agrees, but Daleks Caan, Jast, and Thay rebel, chain up Dalek Sec, and call him a traitor. They decide to replace the human DNA completely with their own, making human beings with Dalek character.
Martha has been studying the plans of the unfinished Empire State Building and tells the Doctor he must remove the Dalekanium panels from the building’s mast to stop the energy collection, but the Doctor drops his sonic screwdriver and ends up holding the mast when the strike hits. The energy flows through him and down the building and awakens the new hybrids.
The Doctor flees to the theatre with the human-Dalek army in pursuit through the sewers. He pleads with the Daleks Thay and Jast to listen to Dalek Sec and let him help. They refuse and try to kill the Doctor, but Sec dies saving him. They order the human Daleks to kill him, but the human Daleks give them an argument. In the gamma strike, some of the Doctor’s Time-Lord DNA transferred to the Dalek hybrids, and that just makes them more antagonistic. The army turns on Thay and Jast and kills them. Dalek Caan kills the rest of the army and flees from the Doctor with an emergency temporal shift.
The BBC would not spring to send the Doctor and Martha to New York, but sent a team to take static shots, from which anything built since 1930 was removed. The Daleks count time in Rels, which are about 1.2 seconds in length, as established in the two 1960s Doctor Who movies with Peter Cushing—about the only thing in these movies to become part of TV canon. Dalek Sec develops a conscience when he combines with humans. The Doctor is filled with rage as never before against the Daleks—Rose died and the Time Lords were wiped out to destroy them, but they still live. He says: “They always survive when I lose everything.” But the childlike and confused Dalek Sec manages to sooth his savage breast. In the end, Sec sacrifices himself to save the Doctor. It’s an emotional roller-coaster ride.