The Doctor attempts to take Rose to Sheffield in 1979 to see Ian Dury in concert, but ends up in the Scottish moors in 1879. They encounter a carriage carrying Queen Victoria, who has been forced to travel by roads to Balmoral Castle as a fallen tree has blocked the train line to Aberdeen. The Doctor poses as Dr. James McCrimmon using his psychic paper, and the Queen invites him and Rose to join her as they travel to the Torchwood Estate to spend the night. Sir Robert MacLeish, owner of the Torchwood Estate, greets the guests though encourages them to continue, but Queen Victoria insists on staying, as the estate was a favourite of her late consort, Prince Albert. Sir Robert gives the Queen, the Doctor, and Rose a tour of the estate, including the Observatory built by his father, a polymath skilled in both science and folklore and who was fascinated by local stories of a werewolf. The guests are invited to dinner by the Steward of the house, and the Doctor tells Rose that she should change into more appropriate garb for the meal, and has her led to a wardrobe.
While looking for an outfit, Rose discovers a servant girl, Flora, hiding in a wardrobe who explains that earlier in the day, a group of monks led by a Father Angelo threatened Sir Robert, and had locked up the rest of the estate staff in the cellars. The monks have taken the places of the servants, with Father Angelo acting as the Steward. Rose and Flora leave to room to get help from The Doctor, only to find that the guards in the house have been drugged and have fallen unconscious. Both women are caught by the monks and chained up with the rest of the staff in the cellar. Rose sees a caged being, previously brought in by the monks, and recognises it as a human possessed by an alien intelligence. She learns from it that the body the being inhabits is that of a local boy, and that it is planning on creating the "Empire of the Wolf" by possessing Queen Victoria.
At dinner, Sir Robert relates his father's studies on the local werewolf stories, though notes that his efforts were resisted by the Brethren of the monastery in St. Catherine's Glen, who may have turned from God to start worshiping the wolf. As a full moon streams in through the windows, Father Angelo starts chanting in Latin — "lupus magnus est, lupus fortis est, lupus deus est" — "The wolf is great, the wolf is strong, the wolf is God", and the Doctor realises that there is immediate danger to all in the estate. Sir Robert apologises to the Queen for his betrayal, saying that the monks were holding his wife, Lady Isobel, and forced him to play the role. The Doctor realises that the fallen tree on the train tracks was a ploy to lure The Queen to the estate in a quest to wrest control of the throne of England, and as the Doctor and Sir Robert race to the cellar, she confronts Father Angelo and kills him. As the Doctor and Sir Robert arrive at the cellar, they find that the monks have opened the cellar doors, allowing the moonlight in and causing the transformation of the possessed being into a werewolf. Rose and the other servants, who have broken free of their chains, flee the cellar as the Doctor locks the door with his sonic screwdriver. The house Steward and the other men attempt to hold the werewolf at bay with rifles, but are unable to contain it and are killed. The women take shelter in the kitchen, allowing Lady Isobel to recognise that the monks all wear mistletoe garlands, likely to ward off the werewolf, and organises the other women into creating a mistletoe broth to be used as a weapon.
The Doctor, Rose, and Sir Robert meet up with the Queen, who is carrying a mysterious box that she had brought with her on the trip, and are chased into the Library by the werewolf. The Doctor recognises that the door and walls of the Library are engraved with mistletoe and covered in viscum album — oil of mistletoe — all likely designed to keep the werewolf from entering the room. The four use the Library to discover that an object fell to Earth in 1540 near the monastery, and though a single cell of the alien being may have survived, it would have become stronger with each generation, passing from host to host, and now at the point of wanting to create its own empire. The Queen, realising she may not escape alive from the situation, asks Sir Robert to find a safe location for her box, containing the Koh-i-Noor diamond, which she was taking to have it cut down at the royal jewellers at Hazlehead. The Queen relates that Prince Albert was always attempting to achieve a better cut for the diamond, and The Doctor, recognising that the Prince had frequently visited Sir Robert's father, surmises that the two were aware of the alien presence and had created the Torchwood Estate and the Observatory as a trap for the creature. The group flees to the Observatory and are chased by the werewolf, but are given a brief respite as Lady Isobel appears and splashes the mistletoe broth on the werewolf. Sir Robert thanks his wife and tells her that he loves her, and instructs her to take safety in the cellar.
The group barricades themselves in the Observatory, but unlike the Library, it is not protected with mistletoe. The Doctor surmises that while the being changes into a werewolf by moonlight, it would be harmed by intense amounts of the light. As the Doctor and Rose attempt to maneuver the telescope into place, Sir Robert sacrifices himself to the werewolf to give the Doctor more time, stating that this should make up for the deception he was forced to commit earlier. As the werewolf breaks into the room and threatens the Queen, the Doctor throws the diamond into the concentrated moonlight generated by the telescope, causing the werewolf to be suspended in mid air. The werewolf reverts temporarily back to its human form and asks the Doctor to end its life by increasing the concentration of moonlight, to which the Doctor obliges. The Doctor notices that the Queen has been cut, but she insists it was just from a splinter. The next day, the Queen dubs the Doctor and Rose as "Sir Doctor of TARDIS" and "Dame Rose of the Powell Estate", but then immediately banishes them from the Empire, as they represent a world of terror and blasphemy and yet they consider it fun. The two return to the TARDIS, with the Doctor reflecting that Queen Victoria's children were found to have haemophilia, and perhaps that was just a Victorian euphemism for lycanthropy. The Queen tells Lady Isobel that her husband's sacrifice and the ingenuity of his father will live on, as she will create the Torchwood Institute to protect the Empire from enemies beyond the imagination.
Doctor David Tennant (Tenth Doctor)
Companion Billie Piper (Rose Tyler)
Pauline Collins – Queen Victoria
Ian Hanmore – Father Angelo
Michelle Duncan – Lady Isobel
Derek Riddell – Sir Robert
Jamie Sives – Captain Reynolds
Ron Donachie – Steward
Tom Smith – The Host
Ruth Milne – Flora
Writer Russell T. Davies
Director Euros Lyn
Script editor Simon Winstone
Producer Phil Collinson
Executive producer(s) Russell T. Davies
Production code 2.2
Series Series 2
Length 45 minutes
Originally broadcast 22 April 2006