"What's a zygon?" Graham asked as Jack and Jenny dragged the fake Yaz into the console room.
"Zygons are metamorphic humanoids. They have the power to impersonate any living creature they please," the Doctor said, seething. "But to do that they have to keep the original imprisoned nearby."
"Which means the real Yaz is somewhere on the moon or planet and will die if we don't find her," Ryan guessed.
"Exactly." The Doctor pulled a matchbox out of the console and held it in front of the zygon. "I like Yaz. And I'm not going to let her die. Tell me where she is and I'll let you go free."
"What if I don't?" the zygon Yaz said defiantly.
The Doctor lit a match and held it close to her eye. She hissed and shrunk back.
"Zygons don't like fire," Jack explained quietly.
"Why'd you have to kiss her?" Jenny asked.
"Venom sacs in the tongue," Jack said matter-of-factly. "It was the only way we could find out for sure it was a zygon."
"Why not ask?" Ryan whispered. "What if it had been the real Yaz?"
"We were pretty confident," Jack said. "Especially when she showed no concern for you."
"Shh," Graham hushed them.
"Seriously, I don't want to hurt you, but believe me I will," the Doctor said. She pushed the match onto the zygon's arm. Yaz's image disappeared, leaving a hulking red mass screaming in pain. "Where is Yaz?" the Doctor demanded.
"On the moon," the zygon hissed painfully.
"I need to know exactly where," the Doctor pressed. "We don't have much time."
She started to push the match toward the other arm.
"Stop! Fine. She is the Sontaran exhibit!"
"We never went to a Sontaran exhibit," Ryan said.
The Doctor raced over to the console. "She must have got her soon after you escaped. Remember that thing you were running from?"
"Oh," Graham sighed. "We should have noticed."
"No fault to you," the Doctor said. "You didn't expect it not to be Yaz. Zygons are hard to spot if you don't know what you're looking for. Also, word of advice, never agree to marry someone if you suspect they might be a zygon. You might be wrong."
"I'd like to hear that story when this is over," Jack said.
"The moon is shifting," the Doctor interrupted suddenly. "It's about to break out of orbit."
"What happens when it does?" Jenny asked.
"It'll tear itself apart. It's like all this energy has been building and building, and now it's about to break free. Jenny, Ryan, down to the doors, now. Get ready to break Yaz free and get her onto the ship. Graham, keep an eye on the zygon."
The Doctor flew over the exhbits, examining them with hyperfocus.
"There," Jack said, pointing. "That's definitely the Sontaran exhibit."
The Doctor landed roughly, and Ryan practically flew out of the bay doors. He ran into the exhibit, looking around.
"Yaz!" he yelled.
"Over here!" Jenny pointed.
Without hesitation, the two of them pulled at the sticky red mass holding Yaz to the wall. Yaz fell forward, gasping for air and choking. Ryan caught her and started to help her towards the ship. The whole moon jilted, and suddenly started moving. The force knocked all three of them to the ground.
"Hurry!" Jenny called, helping Yaz to her feet.
"I can't," Yaz gasped.
"Pick her up, Ryan!"
Ryan picked her up, and with Jenny's support, they made it back to the ship. The Doctor moved the TARDIS into space before closing the doors. The moon exploded seconds later. Yaz, Jenny, and Ryan collapsed on the floor, watching the planet grow smaller as they retreated. Then the TARDIS stopped, and the Doctor's voice sounded over the intercom again.
"I want you all to watch," she said solemnly. "Look at your planet. Watch it burn. Memorize it."
A solar flare surged and engulfed the entirety of Pandloria. The planet burst free of it's orbit control, and spun wildly around the sun, breaking into pieces. The people burst into tears, sobbing and screaming in fear.
"This is what happens when you mess with nature," the Doctor continued sadly. "Your scientists believed you were above it all. No one is above it all. Not even Time Lords."
The TARDIS retreated even further, until all they could see clearly was the sun. The Doctor walked down the stairs slowly, but her voice still reverberated around the chambers.
"Remember this. Your planet was beautiful. It was amazing. It could have been great. Your species could have joined the rest of the universe with glory and honor. But you decided you were better. Now I need you to be better than you were. Be kind. Have compassion. Love others who are different from you. Practice humility. Show mercy as I have shown you mercy. Remember this as you start your new lives."
The sun exploded, turning into a supernova. A shocked gasp rippled through the crowd. The Doctor joined her companions on the edge of the ship, looking out at the stars. Araya slipped her hand into the Doctor's.
"I didn't want it to be this way," she sighed. "I never do. But we must learn from our mistakes. They help us be better."
"Where will we go?" Araya's mother asked.
"I'm taking you to a peaceful planet called Florana. They know you are coming and are preparing a place for you to stay while you start to build a new life for your people."
"That sounds nice," Araya said.
"Yes, it is. I think you'll like it there a lot. I think there was a princess there named Araya. Or maybe that's in the future. Maybe you are the princess, who knows?"
"Thanks for your help, Jack," the Doctor said as she shifted the TARDIS back to normal. All the Pandlorians had disembarked and been taken to the makeshift refugee camp on Florana.
"Thanks for the rescue," Jack grinned back. "It was good to see you again Doctor."
"You could stay with us for a bit if you'd like," she suggested. "We've got plenty of room."
Jack smiled. "Thanks. I really appreciate it. But I've already stayed away for too long. I left a little band of fighters in the Althosian System. I'm sure they're wondering what's happened to me."
"You're welcome anytime," the Doctor said fondly. "It's not good for us immortals to be alone."
"I know. Thank you. But we can't stick with each other forever either."
"Yeah, I guess you're right. Speaking of, have you met Ashildr yet?"
"I've run into her a few times," Jack said, smiling. "She's a good kid."
"That's good, I'm glad you found her. Are you going to say goodbye to others? They just popped off to the kitchen to get some drinks."
"You have a kitchen?"
"Of course I have a kitchen. Why wouldn't I?"
"What do you use it for?"
"I kept fish fingers and custard in there for awhile. Clara used it to make souffles...I don't know, just kitchen things. Is that weird?"
"No, it's normal. Which makes it weird."
The Doctor grinned. "You can go see it if you like."
"Nah," Jack shook his head. "I'll just skip the goodbyes. It makes it easier, ya know what I mean?"
"It would make it easier," the Doctor admitted. "But not saying goodbye makes it harder at the same time."
"You do both," he said pointedly. "Sometimes even to the same people."
"Are you implying something, Captain Jack?"
"Me? Implying something? Never. Come on, Doc, you know me better than that."
The Doctor smiled gently. "Maybe you're right. Maybe I should say goodbye."
"It's up to you," Jack said. "But I know she would appreciate it."
"Thanks."
The Doctor leaned forward and gave him a hug. Jack pulled out his vortex manipulator, entering in the coordinates.
"See ya 'round, Doc."
"See you around, Captain Jack."
Jack disappeared in a blink of an eye.
"Oh, did he leave?" Jenny asked, slowly walking in with a cup of tea. She handed it to the Doctor, who took it gratefully.
"He had people to get back to," the Doctor explained. "How's Yaz?"
"They all went up to the bedrooms for some sleep."
"I don't doubt it. It has been one very exciting day. What about you? Are you alright?"
"I'm fine," Jenny said, leaning against the chrystal wall.
"And...do you have anywhere or anyone to get back to?" the Doctor asked slowly, looking down at her tea intently.
Jenny shrugged. "Not really. I was sort of on my own when I was kidnapped anyway."
"Do you need me to take you anywhere for anything?" Jenny shook her head. The Doctor inhaled deeply, letting the steam from the tea calm her. "Then...would you like to travel with me?"
A slow smile crept across Jenny's face as she nodded slightly. "If it's alright with you...why would I say no?"
"Well...I dunno. Maybe 'cause I've changed, or you've changed."
"You're definitely not what I expected," Jenny said.
"I never am," the Doctor said.
"But you're still the same person, I think." Jenny looked her up and down for a moment. "So...do I just call you 'mum' then, or what?"
"Mum would be great," the Doctor said, setting down the tea. "I like mum."
Jenny stepped forward eagerly and embraced her.
"Me too."