(Just so you guys know, Sky is still passed out on the floor of the TARDIS, and as far as I know, Cassie is still inside.)
Thalia
The Doctor looked stunned when he stepped into the TARDIS. At first I was confused, but then I remembered that he was human. He had the usual reaction, walking out and around the box to inspect it before coming back in again. When he left the second time, he didn't come back.
"Wait!" I yelled and ran out of the house, hoping that was the direction he went in. Rain poured down and soaked my skin, the chill seeping into my bones. Within seconds, my hair was dripping. I looked around, but I didn't see the Doctor anywhere. Only then did I realize I had left Cassie alone in the TARDIS with an unconscious Sky.
I saw a flash of orange in one of the windows and walked inside to see what it was. I looked around, my wet hair and clothes leaving small puddles on the floor as I walked. I peeked through a doorframe to see the Doctor talking to a girl. She had a strange hair colour; sort of like a reddish, orangey-brown. She wore a big blue bow on her head and a blue and orange dress. She seemed to be arguing with the Doctor, but I couldn't make out what they were saying. I watched in terrified fascination as the girl slipped the Doctor's fob watch out of her pocket and handed it to him. Gold light exploded from it when the Doctor opened it, and I followed them as they headed back to the TARDIS.
I hid behind another doorway and watched them walk into the TARDIS. I still couldn't hear their conversation, but I caught one name: Niji. I remembered that name, and it meant bad news. I hoped the Doctor didn't still want her back, because I couldn't think of any way that would be possible, besides doing what I proposed earlier. I didn't want to admit it, but I was sort of against the idea of risking my life for someone I didn't even know. I could tell she meant a lot to the Doctor and I didn't want to tell him that she couldn't come back, but it was true.
I heard the sounds of the TARDIS taking off and ran in just a split second before it disappeared. The Doctor was still talking to the girl inside.
(Also, I would've just kept Thalia in the TARDIS, but I had already written the first part of this post a couple days ago and I didn't get to finish it until today, but I didn't want to rewrite the whole thing, so yeah.)
"When you run with the Doctor, it feels like it'll never end. But however hard you try, you can't run forever. Everybody knows that everybody dies, and nobody knows it like the Doctor. But I do think that all the skies of all the worlds might just turn dark if he ever, for one moment, accepts it."
-River Song
"You know when sometimes you meet someone so beautiful and then you actually talk to them and five minutes later they're as dull as a brick? Then there's other people, when you meet them you think, 'Not bad. They're okay.' And then you get to know them and... and their face just sort of becomes them. Like their personality's written all over it. And they just turn into something so beautiful."
-Amelia Pond