Dalek

The TARDIS is drawn off course by a distress signal, and materialises in a bunker in Utah, 2012. The Doctor and Rose Tyler find that the bunker is a museum, full of alien artifacts. An alarm is immediately set off, and they are taken to see the owner of the Vault — Henry van Statten, a billionaire collector of alien artifacts. Impressed with the Doctor's extraterrestrial knowledge, he invites the Doctor to see the "Metaltron", a creature he claims is the last of its kind. The Doctor enters the "Cage", where the creature is held, and begins to speak to it, offering his help. The creature responds by snarling in fury at him. The Doctor realises in horror it is a Dalek. Initially terrified at its threats of extermination, the Doctor is delighted to discover the creature is damaged and helpless, and attempts to kill it to purge the Dalek race forever, before being stopped by van Statten's guards.
Meanwhile, Adam Mitchell is showing Rose around the base. Adam shows her the Dalek, being tortured by a technician to force it to speak. Sympathetically, Rose asks to be taken down to the Cage to help the Dalek. Rose then touches the Dalek casing, which immediately absorbs her DNA and background radiation (a radiation that is picked up in mass quantities from time travel, and is the Daleks' sole power source). It escapes from its cage and downloads the entire internet, realizing that it is the only Dalek left. In response, the area is evacuated, and guards focus fire upon it, to no effect; the Dalek swiftly exterminates the guards. The Dalek demands to speak to the Doctor, and tells him that it was able to regenerate its casing, but was unable to find any other Daleks or orders, and will follow the default function: the extermination of everything in its path.
As Rose and Adam are escaping from the Dalek, the Doctor tries to stall to save them. Adam escapes, but Rose is cornered by the Dalek and is seemingly exterminated. Horrified, the Doctor blames van Statten for everyone's deaths. However, the Dalek has not killed Rose, as her DNA is making it hesitant. It instead negotiates, trading her life for access past the bulkheads which are obstructing its way. The Dalek then travels to van Statten's office, and is about to kill him before Rose intervenes and offers the Dalek its wish: freedom.
On the highest level of the museum, the Dalek creates a hole and opens its casing to directly feel sunlight for the first time. The Doctor arrives, gun in hand, and orders Rose to move. Rose refuses; the Dalek is changing, as it could not kill her or van Statten. Appalled at his own actions, he lowers his weapon. Both he and the Dalek realise that the Dalek is mutating further, and is becoming unable to conform to the Dalek objective. It asks Rose to order its death, and after being given the order, annihilates itself.At the end of the episode, van Statten's assistant Diana Goddard orders van Statten's mind wiped and the vault filled with concrete. At the TARDIS, the Doctor ruefully observes that as the last survivor of the Time War, he "wins". He also tells Rose that he would be able to sense the presence of other Time Lords had they survived. Adam then comes by, telling the Doctor that Goddard is sealing the base. Rose invites Adam aboard the TARDIS, which he enters with a puzzled expression before it dematerialises.