Kaylee smiled, thinking about last night and taking another bite of her caramel apple. "Hey, Doctor", she said. He raised an eyebrow in response and reached into his paper cone before snatching back his hand. The chestnuts were still too hot to handle. "You say you've travelled all around the 'verse. Have you ever seen anything like that lake last night?"
They were walking along the boardwalk between the beach-side resort city and the lake that brought millions of tourists there every year. The sun had risen a couple hours ago, and with it the magical blue glow of the lake had faded to invisibility. Since then, they had been walking past vendors and street performers as the crowd of the night before dissipated to become the late-sleepers of today in the local hotels.
The Doctor smiled wistfully. "Well", he started, "I've seen some pretty amazing beaches. I've seen one with gemstones instead of sand. I've seen one with pink water underneath green skies. I've been to a planet that only has two days for every year and no moon, so the ocean is completely underground for half the year. True story. There's a huge gathering there four times a year to watch the tide come in. You can see the sand go from white to dark grey, then finally the water just sort of bubbles up through it and everyone goes crazy. It's amazing."
"Oh", Kaylee responded, disappointed. "Well, I thought it was something special." She took another bite of he apple, but with less enthusiasm.
"But it is!", the Doctor said, trying to re-kindle her spirits. "Sure, if you see the same amazing thing long enough it starts to lose its appeal..." He extended his arms and turned 360 as they continued to walk. "You notice it's all tourists here. The only locals are the ones making money off of them. But on the other hand, you can see all sorts of amazing things - different things - and never get bored of them. For example, if I told you there were another lake on another world, and this one glowed orange in the moonlight, you'd want to see it, wouldn't you?"
"Well... I suppose you're right." She munched some more apple, then spent a moment sucking the caramel out of her teeth as the two walked along in silence.
"Is there?", she finally said.
"Is there what?", the Doctor inquired idly as he fished a chestnut out of his cone and began shelling it with his teeth.
"Is there a lake like that. You know, orange?"
The Doctor spit out the last bit of shell and smiled cheekily. "Not that I'm aware of." He popped the chestnut into his mouth and chewed for a few moments before stopping. "Still, it's a big universe. It could be. It could be."
The two of them reached the Tardis just then, and the Doctor turned his key in the lock and opened up the door for Kaylee. She entered, and he followed. He removed his coat and threw it over the railing, then ran past Kaylee to the console.
"Okay, now that we've got the short jump out of the way, what's the real destination?", the Doctor asked.
"What do you mean?"
"Oh, come on... This place was nice and all, but you could have hopped a shuttle from any of the central worlds if that's all you wanted. You're on the Tardis now. A ship unique in all the cosmos. You can visit any time and any place in the whole of the universe instead of just these five stars. Hanging Gardens of Babylon? I've got a sitting reservation with a terrace view. Bone fields of Masador strike your fancy? I know a man at the potter's tent who owes me a favor. Want to meet the Queen of Peladon? I'm an old family friend." As he spoke, he walked around the Tardis turning knobs, setting levers, flipping switches and pushing buttons. At one point he even pounded a bell with a little mallet. Then he stopped and leaned over the console, looking her in the eyes. "So, Kaylee, challenge me. Where to next?"
Kaylee thought for a while. She perched on the railing that ran all the way around the console and considered. Most of those places didn't mean anything to her. She'd heard of Babylon, but she'd feel like a fool if she picked one of the three places he'd mentioned after he offered her infinity. So she started thinking about what she actually wanted. And it came to her. She smiled and looked at the Doctor, challenging him.
"Apples", she said.
"Apples", the Doctor repeated. Then as if he had only just heard her, and couldn't have properly understood, he asked, "Apples?"
"Yeah, apples." Kaylee got down off the railing and walked around to the Doctor. She held up the apple core she had been gnawing on, still attached to the stick, then she grabbed his hand and stuck the core in it. "Apples." She walked past him and started pacing in a circle around the console. "Did you know that every single apple in the Tauri system comes from a single tree brought here on a single generation ship? The branches have been grafted and cloned and spread throughout the system, and sure, there are regional differences because of soil quality or minerals in the water, or light levels, but essentially, every apple that anyone alive has ever eaten has been basically the same apple."
She stopped and made eye contact with the Doctor, then turned and paced in a counter-clockwise circle around the console. "But the story that gets passed down is that this type of apple was once just one of hundreds, maybe more. There were red apples and pink apples and yellow apples, sweet apples and sour apples, firm apples and soft apples, some good for baking, some good for pickling. And all these apples were common back on Earth-That-Was." She stopped again and looked up at the Doctor. He wore a rather confused expression.
"Yeah, I've been meaning to ask you about that. Why do you call it that? 'Earth-That-Was'?", he asked.
Kaylee half-coughed, half-laughed. She wasn't sure why she was being tested; surely he knew the history, same as anyone. For the moment though, she decided to play along. "Okay...", she said hesitantly, "Humanity was making great technological advances, but discovered too late that it all came at a price. They had out-mined all their resources and polluted the land and water to the point where the world was no longer livable. The magnetic field was out of whack and tectonic plates were breaking up. So they built these huge generation ships and left the Earth just before it was destroyed."
"Sorry, what was that?"
"The ships managed to get the last of humanity away just before the Earth was destroyed in a fiery explosion-"
"No it wasn't", the Doctor said with a confused expression.
"Sure it was. There are tales of the last ship leaving riding the pressure wave from the-"
"No. It wasn't. It's still there. Sure, it was polluted, with a poisonous sky, and humans couldn't live there anymore, mostly because of the temperature, but it wasn't 'destroyed'. That's not even how physics works, by the way", the doctor explained as if telling a child that the tooth fairy wasn't real. "And without humans there killing it, the Earth got better. Even now, there are people returning."
"I'm sorry Doctor, but you are full of DIO-se. You may as well be saying there was never an Earth at all."
"Well then, Kaylee", the Doctor said with a smile, "I know where we're going. Prepare to see Earth-That-Is for yourself." The Doctor ran around the console idly flipping switches, then pulled back on a large lever and the central column rose and fell to the grind of the engine.