The Doctor looks back at the house of Martha Jones with longing on his face. She has decided to stay home and now he must travel on his own. If only the Master hadn't died, then he could have helped the mad Time Lord. But, it was not to be so. And so, the Doctor enters the TARDIS and continues to travel alone.
Far away in a different galaxy, a stasis chamber is hidden in a place that no one has found except for the occupant. But her peace is soon to be destroyed as the planet's inhabitants dig closer and closer to her.
"Hello? It's time to wake up and tell me who you are." The Doctor gently shakes the girl's shoulder as she continues to sleep as if she was in her stasis chamber. He pulls out his sonic screwdriver and examines her. "Human…" Alarm crosses his face. "What's a human doing here?" He jumps away from her towards the chamber's computer. "It's impossible," he murmured. The Doctor scrubs his hand through his hair. "Well, I'm not going to leave her here." He gently picks her up and carries her into the TARDIS. After placing her on the couch, he quickly calibrates the TARDIS and dematerializes as the caves and tunnels collapse, burying the girl's stasis chamber.
When they landed, he draped his long coat over the girl and whispered, "I'll be right back." The Doctor leaves the console room to confront those responsible for the cave in.
"We didn't know there were life forms down there," the leader of the drillers says.
"You didn't know that there are thousands of colonies only 500 miles under the surface?! You didn't scan." The Doctor gets in his face. "You will integrate all of those people into this world and you will take care of them." Without another word, he returns to the TARDIS and sets course for Earth.
"Where are you taking me?"
He glances over his shoulder to see the girl sitting up, wearing his coat as if it was her own. "Oh good. You're awake. I'm taking you home."
She shakes her head and crosses her arms. "Impossible. My home is long gone."
"Nonsense." He gives her a big smile. "The earth is alive and thriving."
"I'm telling you. My home is long gone, destroyed. It has been for a long, long time."
A thoughtful look crosses his face. "You can't be a colonist. We're still in the early twenty-first century," he murmurs. "Why are you only asking where I'm taking you? Aren't you curious about where you are?"
The girl smiles. "That's easy. I'm in a timeship with space traveling capabilities, also known as a Time and Relative Dimension in Space. TARDIS for short," she rattles off and giggles at his dumbstruck face. "You aren't the first Time Lord I've encountered."
"What's your name?"
"The Constant, but you can call me Constance, and you are the Doctor."
He tenses and stands up straight. "How do you know all that?"
"The fob watch will explain everything," she says pointing at the watch by his hand. "It can only be opened by a Time Lord. It will tell you everything and restore me to my true self. Do not worry. It isn't dangerous to either of us. It's just memories of a time long past and what I saw in the time vortex."
The watch does explain everything, but Constance faints as soon as it is opened. Once he is released from the flood of information, the Doctor cradles her in his lap. "I thought you were a myth," he whispers, brushing her hair from her face.
And she sleeps for the next week. This gives the Doctor plenty of time to think about what happened. He thought the Chameleon Arch was the only way for a Time Lord to change their DNA. It came with the side effect of forgetting who they were while saving their lives. But this girl was able to keep her memories and change her DNA.
The only thing that brings him from her side is a sudden alarm. He runs to the control room and struggles to maneuver the TARDIS through a meteor storm. "Come on, come on, come on!" he mutters when suddenly it becomes easier.
"Don't you know that it's dangerous to fly alone?"
"What?" He quickly looks to the other side of the console to see Constance standing there with her hands on the levers, smiling as if it were Christmas. "How…? I…"
"Sorry, the alarm woke me. It's been ages since I've flown with my parents. Oh, how I've missed this!" Together, they skillfully land in a park in London. "So, what are we going to be doing today?" He just stares at her. "Can we go see the Eye? I've always wanted to go on a Ferris wheel! Humans have such strange ways of entertaining themselves." He looks down at her hospital style clothes. "Do you think the TARDIS might have a change of clothes for me?"
"I don't know what to make of you," he mutters.
"You know that you mutter a lot, right?" she laughs.
"You're a myth come to life."
"Right when it was time," she says, becoming serious for him. "You didn't find me by chance."
"No, I didn't. Strangely enough, glow worms lit my way to you."
She nods. "Mother was able to ask them to light the way for the Time Lord with the blue box."
"I wasn't even planning on stopping there," he mused.
"Your TARDIS brought you there. She knew where you needed to go." Constance walks closer to him. "In the vortex, I saw you as the last of the Time Lords, left to travel alone for the rest of your days. But I saw a way for that to change, for you to have something consistent in your life."
"You gave up living your life with your family and friends to be the constant in the life of a man who might not have welcomed you in?" He looks at her incredulously.
She lays a hand on his arm. "There are some things that just need to be and it is never good for a Time Lord to be alone."
"But surely you have many regenerations left, if not all." Sadness and pity creep into his eyes. "I only have two left. Once those are gone, you'll be the one that's left alone."
"Let me be the one to worry about that." A smile crosses her face and she jumps back and gives a clap of her hands. "I'm going to see if the TARDIS has any clothes for me, and then we can go see the Eye."
The Doctor looks outside. "We may need to postpone that trip to the Eye."
"What for? If it's a long line, I'm sure we can wait a bit," she calls from down the hall, feeling guided by the TARDIS to the wardrobe.
"Weeelllll…."
"Doctor," she says in a no nonsense tone. She pops her head around the corner. "What's wrong?"
He leans away from the door and faces her direction with a confused look on his face. "Um, well. I think I just saw fat walk by."