The Doctor visits various points in time to watch Clara grow – from 1981, when a stray leaf brought her parents Dave (Michael Dixon) and Ellie (Nicola Siân) together, to 2005, when Clara’s mother Ellie died. Clara has kept all these memories in a book, 101 Places to See.
In the present day, the Doctor whisks Clara off to the rings of Akhaten to witness the Festival of Offerings, a holy celebration in which aliens from seven worlds come together every 1000 years to pay their respects to the Old God, whose mummified remains are kept in a holy pyramid on asteroid orbiting the planet.
While exploring a local bazaar, Clara meets young Merry (Emilia Jones), the Queen of Years, who is the vessel of all Akhaten history and who was selected at birth to sing a lullaby, The Long Song, at the festival. After calming Merry’s nerves, Clara heads to the amphitheatre with the Doctor to watch the ceremony.
Merry, and a Chorister inside the pyramid, sing the lullaby while gifts of bounty are offered up. When the Chorister hits a wrong note, the Old God is stirred and a tractor beam pulls Merry toward the pyramid. Clara and the Doctor reach the asteroid on a moped that Clara is able to rent only after giving up her mother’s ring.
Inside the pyramid, the Doctor and Clara learn that the Old God is an eater of souls and that if Merry is not offered up as a sacrifice, then the Old God will escape and consume the entire universe. Clara helps Merry escape and return to the amphitheatre where the young girl leads the audience in singing the lullaby. The Doctor, meanwhile, offers up his own painful memories to the Old God hoping it will satisfy its hunger. But it is actually the leaf that Clara carries in her book that eventually halts the ravenous parasitic entity. The infinity of ‘what if’s’ in the days that never came following Clara’s mother’s death is too much for its appetite…
The episode ends with Clara returning home, where the Doctor returns to Clara her mother’s ring.
