In Victorian London, a dinosaur materializes and spits the TARDIS onto the banks of the river Thames, ushering in the freshly-regenerated Twelfth Doctor Peter Capaldi and Clara Oswald Jenna Coleman. They are greeted by the Paternoster Gang, a remarkable trio consisting of Silurian Madame Vastra Neve McIntosh, her human wife Jenny Flint Catrin Stewart, and the Sontaran butler Strax Dan Starkey. The Gang helps calm the bewildered dinosaur and escorts the Doctor and Clara to Vastra’s residence, where the Doctor rests and Vastra challenges Clara about her prejudices toward the Doctor’s changed face. Clara confesses that she is struggling to adapt to the new Doctor, whose appearance and demeanor feel markedly different from the man she knew.
The Doctor awakens to hear the dinosaur’s pleas for help before it unexpectedly bursts into flames. He joins Clara and the Paternoster Gang at the river and learns that this strange spontaneous combustion isn’t an isolated incident. A striking, unfazed man across the river draws the Doctor’s eye, and he dives in to investigate while Clara and the others start their own inquiry back at Vastra’s home.
The next morning, the Doctor roams the backstreets in search of answers about how his body chooses a new face during regeneration. A newspaper hides a clue—an article stamped with the phrase “The Impossible Girl”—directing them to a fashionable restaurant where they reunite. Yet they quickly realize neither of them planted the message, and the room is filled with robots meant to keep them from leaving. They are pulled into a hidden lair where the unfazed man stands among idle, human-like bots. The Doctor deduces that this man is a long-lived cyborg, attempting to become human by replacing parts with biological ones drawn from victims of spontaneous combustion, including the dinosaur itself.
The Doctor leaves Clara as the robots and the cyborg begin to awaken. Remembering his own hard-won guidance, Clara holds her breath to hide from the approaching machines, but she’s captured and brought before the cyborg. He explains his quest for a “promised land” by prolonging his life through ever-more replacement parts and questions Clara about the Doctor’s whereabouts. The Doctor returns with the Paternoster Gang to confront the robots and pursue the cyborg back to the restaurant. In a shocking turn, the cyborg releases a hot-air balloon made of human skin, lifting the restaurant into the sky with him and the Doctor aboard.
During the confrontation, the cyborg reveals that he and portions of the restaurant originate from the SS Marie Antoinette, the sister ship to the SS Madame de Pompadour, a nod to the Doctor’s past adventures. The Doctor warns that the cyborg must either kill himself or be stopped to protect the humans. Moments later, the cyborg plummets from the balloon and is impaled on the spire of Big Ben, leaving the remaining robots lifeless.
After regrouping, Clara discovers that the Doctor and the TARDIS have vanished. Vastra reassures her that the Doctor will return, noting that Clara—the person who knows the Doctor best—will be ready to move forward with or without him. The Doctor does reappear, but not to take Clara home; instead, he emerges in Glasgow. A phone call from the Eleventh Doctor [Matt Smith] to Clara, felt moments before his own regeneration, nudges her to stay by his side for now.
In the epilogue, the cyborg awakens in a beautiful garden and meets Missy [Michelle Gomez], a mysterious woman who calls the Doctor her boyfriend and hints that the cyborg has finally reached his promised land.
