Thousands of aliens are in orbit about the planet Trenzalore, from which a message is broadcast across Time and Space. The Doctor (Matt Smith) and Clara (Jenna Coleman) are asked to explore the planet beneath the force-field laid down by the Church of the Papal Mainframe, headed by Tasha Lem (Orla Brady).

The message comes from a human colony called Christmas. There is a crack in reality in the clock tower, sent by Time Lords. They are trying to escape the pocket universe the Doctor put them in. They want him to announce his name as a sign it is safe to emerge. The aliens dare not attack, lest the Doctor let the Time Lords out, but the Doctor cannot leave, or the aliens will burn the inhabited planet to stop the Time Lords.c The Doctor tricks Clara into returning to Earth, but she jumps onto the TARDIS as it returns to the Doctor, 300 years later, his time. He reveals that he has no regenerations left and is ready to die defending Trenzalore. The Papal Mainframe is now called The Church of the Silence, a chapter of which broke off to interfere with the Doctor, causing the crack in the tower. After rescuing Tasha Lem from the Daleks, the Doctor tricks Clara again into returning to Earth.

More centuries pass. The forces of the Silence are dwindling and only the Daleks remain. Tasha brings Clara back to Trenzalore as the siege ends. The Doctor is dying of old age and cannot stop the Daleks. After saying good-bye to Clara, he climbs the tower to face his enemies. Clara speaks to the Time Lords through the crack, begging their help. The crack appears in the sky and regeneration energy flows into the Doctor. With his power, he destroys the Daleks. The crack closes, the stalemate ends, and to Clara’s amazement, the Doctor regenerates into the Twelfth Doctor, played by Peter Capaldi.

Karen Gillan appeared as Amy Pond. Both she and Matt Smith had basically shaved their heads for other roles, she for Nebula in Guardians of the Galaxy, and they had to wear wigs. The crack in the sky is the same shape as the mountains behind the town of Christmas. This was the 800th episode since the beginning in 1963. Matt Smith was reduced to tears during the read-through of the goodbye. An unknown child actress played Young Amelia Pond, because Caitlin Blackwood was a teenager by this time. The Doctor lives 900 years during the story. Among the Doctor’s enemies are Daleks, Cybermen, Weeping Angels, The Silence, Sontarans, Judoon, Silurians, Terileptils, and the Raxacoricofallapatorians. Regeneration scenes keep getting more spectacular. This one was so powerful it killed an army of Daleks. The episode was highly praised and provided a powerful send-off for Doctor Eleven.