"So, Doctor, where are we going today?" Catherine asked. "I have the whole universe to show you. You're the guest, you choose." He said with a big smile. It was the very first time he smiled since he had lost Donna. He had travelled alone for quite a while, after she died to save him, not wanting anyone else to perish because of him. The Master was right. People were willing to give their lives to save his and he couldn't figure out their reasons. Ok, he was the last of the Time Lords but this didn't make him a special person. Still, he really needed someone to stop him, to help him out when the power was overwhelming and so were sadness and remorse. He had found Catherine a few days earlier, in Paris. It was the 23rd of December and it was snowing, real snow for the first time since the day he had met Donna. He was happy, there was no trouble, he was just taking a stroll under the snow and he had seen her. She was crying at the corner of the street. He went to her, grabbed her hand and said in a gentle tone: "Run". She had followed him ever since. Catherine had told him she had never found a place in the world and that she was completely alone. They became mates and he took her to see the stars, promising not to make her go back.
"Well" – she said – "I want to go far across the universe, I want you to take me somewhere so far from earth that it could be only reached with the TARDIS." Then she smiled. She was so sweet, so similar to all of his former companions. She had a bit of each and every one of them and he was happy to have her next to him. They were good friends even after spending just a few days together. "Then I think I know where to take you. You want to have some fun, don't you? Krisiopea, then." – he said pushing buttons and lowering levers. – "Allons-y!" and it all started then.
When they exited the TARDIS, they found a nice deep blue grass waiting for them. The city was composed by glass skyscrapers but they were all upside down, seemingly floating in the sky. Four suns were burning above their heads, making the glass shine brightly. There were many red, yellow and violet trees and strange bushes and flowers. Catherine smelled a sweet perfume of lemon drops and brackish water. "Deep sea grass" the Doctor said taking a bit of the blue grass in his hands and stroking it between his fingers. "And" – he added kneeling on the grass and licking the dirt beneath it – "Lemon dirt. Brilliant!" "So, Spaceman, what exactly is this?" she asked gesturing around her. "This, my dear Catherine Toulon, is Krisiopea, a planet of the solar system of the four suns, third in line. We're on the other side of the universe, in the confederation of Light. This whole planet is three times bigger than Earth and it counts one hundred billion creatures." "How can it count so many people?" she asked, sceptic. "I said creatures, not people. The population of this planet is divided in more levels, each and every of which gives home to a different species. Even the fluid core of the planet is full of life. But you want to have fun, so there" – he said pointing his finger to the skyscrapers – "is exactly where we're going. Allons-y!" he exclaimed holding her hand and running towards the city of glass.