Doctor: David Tennant (Tenth Doctor)
Companion: Billie Piper (Rose Tyler)
Camille Coduri – Jackie Tyler
Noel Clarke – Mickey Smith
Zoë Wanamaker – Cassandra
Sean Gallagher – Chip
Doña Croll – Matron Casp
Michael Fitzgerald – Duke of Manhattan
Lucy Robinson – Frau Clovis
Adjoa Andoh – Sister Jatt
Anna Hope – Novice Hame
Simon Ludders – Patient
Andrew Hopkins - White Patient
Struan Rodger – Face of Boe
Directed by James Hawes
Written by Russell T Davies
Script editor Simon Winstone
Produced by Phil Collinson
Executive producer(s) Russell T Davies
Incidental music composer Murray Gold
Production code 2.1
Series Series 2
Length 45 minutes
Originally broadcast 15 April 2006
The Doctor takes Rose to the farthest point he's ever taken her, to the year five billion and twenty-three in the M87 galaxy. After the destruction of the Earth, humanity settled onto a world they named "New Earth". The Doctor is summoned to Ward 26 in a hospital in New New York through his psychic paper. In the Ward, the Doctor meets several humanoid feline nuns of the Sisters of Plenitude who are overseeing the patients. The patients catch the attention of the Doctor because they all have incurable maladies but are somehow being cured by the Sisters. The Doctor recognises the Face of Boe, who sent the message the Doctor received. Meanwhile, Rose is separated from the Doctor and brought to the basement, where she is escorted by Chip to meet Lady Cassandra. Chip has been using the hospital facility to care for Cassandra, but she is suspicious of the methods used in the hospital and needs Rose's help to investigate. Rose is tricked into stepping into a psychograft, a machine that allows Cassandra to implant her mind into Rose's body possessing her. Examining her new appearance, Cassandra is initially disgusted by Rose's "Chav" outfit but soon decides she is attractive enough. She is able to access Rose's thoughts and learns of the Doctor's new form.
The Doctor is suspicious of Cassandra/Rose's actions after she kisses him and displays knowledge of advanced computer systems. He and Cassandra/Rose discover that the hospital houses thousands of pods containing artificially grown humans in what is supposedly the hospital's intensive care unit. The artificial humans are forcibly infected with every disease in the galaxy so that the Sisters can discover the cures. The Doctor confronts the Sisters over their atrocity, and they insist it was necessary to deal with the influx of settlers and the diseases they brought with them. They also insist that they are simply flesh due to their origins, without any actual life. The Doctor believes that Rose's current actions are a result of being a test subject and orders her affliction to be reversed, but Cassandra/Rose uses a perfume gas hidden in her cleavage to knock the Doctor out, locking him in a pod. Cassandra/Rose then approaches the head Sister and demands payment in exchange for keeping the human test subjects secret. The Sisters refuse, and Cassandra/Rose releases the Doctor and some of the humans as a distraction. The infected humans release others from their pods and soon a zombie-like attack begins, with those infected trying to attack others in the hospital.
A quarantine is ordered, and the Doctor, Cassandra/Rose, and the remaining Sisters try to flee the lower levels. Cassandra is able to jump her mind between other bodies, including one of the infected humans, and learns that the infected humans feel a strong sense of loneliness of not being able to touch or be touched. Eventually, the Doctor and Cassandra/Rose reach Ward 26 and grab all the intravenous medical solutions, emptying them into a disinfectant shower. They are able to spray the mixture onto a group of the infected humans, who within moments become cured of their diseases. The Doctor encourages them to go and spread the cure to the other infected people, and soon the attack is over. The police arrest the surviving Sisters, while the Face of Boe tells the Doctor that the message for him can wait until they meet for the third and final time.
The Doctor orders Cassandra out of Rose's body. Cassandra doesn't want to die, and Chip volunteers to accept her consciousness. Chip's cloned body begins to fail, and Cassandra finally accepts her impending true death. The Doctor decides to do one last thing for Cassandra and takes her back to see herself on the last night someone had called her beautiful. Cassandra/Chip approaches the Lady Cassandra at a party and tells that she is beautiful before collapsing and dying in the younger Cassandra's arms. As Cassandra finally dies, the Doctor and Rose silently leave in the TARDIS.