While waiting for Clara to join him on his adventures, the Doctor pays a visit to her past. He observes everything from the moment her parents meet to the day of her mother's funeral. Clara seems like a perfectly ordinary girl, which just makes her all the more mysterious to the Doctor.
When Clara boards the TARDIS, her only request is to visit somewhere "awesome," so the Doctor takes her to the Rings of Akhaten. It's composed of seven mini-worlds that orbit the somewhat dark sun Akhaten. The Doctor and Clara arrive at the time of a festival of sorts, when specially chosen people sing a lullaby to keep their godly "grandfather" asleep. One of the chosen singers, a little girl named Merry, gets stage fright and flees from the arena of her impending performance. Calling on her innate skills with children, Clara finds her and reassures her everything will be just fine. Bolstered by her new friend, Merry returns to her duties and begins to sing.
Something goes horribly wrong. Merry is plucked away by some invisible force and drawn into a temple that orbits Akhaten. This, the people believe, is where Grandfather sleeps. He turns out to be a scary monster in a plexiglass cage, and although he's been snoozing for all these millennia, he has now started to awaken. The Doctor and Clara zip off to rescue the girl, but discover that the monster isn't Grandfather after all, but rather Grand Pappy's alarm clock. The real recipient of all those songs is Akhaten itself, which the Doctor calls a "parasite god." It feeds on memories and stories and potential, and what better to feed it than a little girl full of potential? When Akhaten awakes, it resembles a super-sized Jack O' Lantern.
To smash that pumpkin, the Doctor tries to feed it his own memories. That's 1000+ years of war and adventure and death and life. The planet feeds on him, but it's not enough. That's when Clara steps in and offers her leaf to the sun. Remember the leaf from her book? Her parents saved it from the day that they met each other, and passed it on to Clara. It represents all the infinite possibilities snuffed out when her mother died. This not only feeds Akhaten, but miraculously overfeeds it, sending it into the biggest food coma of all time, and thus saving the day. Except that now the people living there now don't have any light, but whatever. Stay tuned for the full weecap.
A young man walks down a windy, tree-lined street while trying to read the map he's holding. From a short distance away, the Doctor watches him. The Doctor is reading a magazine from 1981, handily letting us know the year in which the scene is taking place. A leaf falls from a tree and plasters the young man's face. Surprised, he staggers into the street and right into oncoming traffic. A young woman pulls him to safety. They instantly fall in love. We - and the Doctor - follow the course of their relationship. The young man saves that leaf because, as he explains to his beloved, it represents all the millions of little things that had to happen in order to lead to the moment they met. He calls it the most important leaf in human history. How could a girl not fall for that? As the years go by, they have a baby girl, to whom the new mom reads from a book called 101 Places to See. The girl, of course, is Clara. Kudos to the wardrobe department for unearthing all that acid-wash denim. Kudos. At one point, the Doctor gets a little too close to his subjects and gets a ball kicked in his face. "Are you all right?" Clara's mother asks. "Fine," he says. "Marvelous! Refulgent!" It's all smiles and happy times...
...and then it's not. Teenaged Clara stands at her mother's graveside, tears streaming down her face as she clutches the book to her heart. Her father puts an arm around her. The Doctor watches for a while from a safe distance, then retreats to the TARDIS. "She's just a girl," he says. "How can she be?" He looks at a picture of her as the Victorian governess. "She's not possible," he decides.
Adding to the overall mystery is just how lightly she's packed for their adventures. When he picks her up at the Maitland family home, all she has is a cute little satchel and her book. She flits about the TARDIS, amazed and delighted at it all. He tells her they can go basically anywhere in space and time. "So, where do you wanna go?" he asks. The possibilities all but overwhelm her. She thinks and thinks, and thinks some more. "What I would like to see is... something awesome!" That narrows it down a bit.
A few moments later, she's led out of the TARDIS with her eyes closed. "Can you feel the light on your eyelids?" the Doctor asks her. "That is the light of an alien sun!" When she opens her eyes, she sees that they've parked on an asteroid - one of countless others - around a dimly glowing sun. "Welcome to the Rings of Akhaten," he says. On one of the larger asteroids is a pyramid that glows gold. "It's a holy site for the Sun Singers of Akhat," he explains. He goes on to say there are seven worlds in orbit around the sun, all sharing in the belief that life originated on that chunk of rock. He calls it a planet, but I think planetologists would disagree with him. It looks like a smallish mountain adrift in space.