The Doctor (David Tennant), Rose (Billie Piper), and Mickey (Noel Clarke) explore a derelict spaceship some time in the 51st Century. The Doctor finds a time window which acts as a doorway into another space and time. He looks through a French fireplace to see a young girl called Reinette (Sophia Myles) living in 18th Century Paris. He steps through to find that months have passed on the other side.
There is a clockwork service android in 18th Century clothing in her room and the Doctor saves her from its clutches. There is also a horse on the ship that passed through a time window from somewhen. He calls it Arthur. The next time he goes through, Reinette is a young woman and he kisses her. He realizes she is Madame de Pompadour, mistress of Louis XV.
The ship is full of time windows to Reinette’s life. He saves her from an android. The android says that the ship’s androids killed the crew to use their organs to repair the ship. The Androids plan to open a window to Reinette at the age of 37, as her brain will then be compatible with the ship. All this time, Rose and Mickey have been wandering around the ship, getting themselves in and out of peril with the androids.
The clockwork androids show up at a costume ball in Versailles and take Reinette hostage. The Doctor cannot enter the 18th Century now through the time window—in the form of a huge mirror—without being stranded there. But the androids threaten to decapitate Reinette, and the Doctor, mounted on Arthur, crashes through the mirror to save her. The androids can no longer return to their ship through the window and they shut down.
Reinette tells the Doctor that she had her fireplace moved to Versailles, hoping for his return. He finds that he can get back to the ship through the fireplace. He tells Reinette to prepare to leave and he will be right back, but when he does return seven years have passed and she is dead. King Louis gives him a letter she wrote. He returns sadly to the ship, named SS Madame de Pompadour.
Sophia Miles did not try out for the role of Reinette, she was offered it. Later she became David Tennant’s girlfriend. The story was nominated for the 2006 Nebula Award and received the 2007 Hugo. The clockwork androids were particularly praised. The scene of the horse crashing through the mirror was complex and difficult. Two different horses were used, and Tennant’s head had to be superimposed on the stunt-rider’s body. According to urban legend, the wineglass used was based on the shape of Madame de Pompadour’s left breast. Her real name was Jeanne Antoinette Poisson. Sophia Miles’ gold- and jewel-encrusted gown had been worn by Helen Mirren in The Madness of King George. The spaceship was shaped like a key. The time window is said to have been inspired by The City on the Edge of Forever in Star Trek: The Original series.