Inside the sweltering tunnel, the time travelers caught their breath. The Doctor kissed Rose on the forehead. "Jeopardy friendly." He muttered into her hair.
Donna shook her head as she stood up, "You fought her off with a water pistol. I bloody love you."
The Doctor started down the tunnel, holding tightly to Rose's hand. "This way." He called behind him.
"Where are we going now?" Donna asked, following behind the couple.
"Into the volcano." The Doctor said as if it was the most reasonable request in the world.
Donna emphatically shook her head. "No way."
"Yes, way. Appian way."
"Why does this feel like a Ms. Frizzle field trip?" Rose muttered under her breath.
They started walking through the vent tunnels, and the heat grew harder and harder to bare, and Donna felt it the worst.
"But if it's aliens setting off the volcano, doesn't that make it all right for you to stop it?" Donna asked with a cursory glance at Rose. She hadn't forgotten their earlier conversation, but she still couldn't see why they couldn't interfere.
"Still part of history." The Doctor answered over his shoulder.
"But I'm history to you. You saved me in 2008. You saved us all. Why is that different?"
He shook his head. It wasn't very easy to explain, and his focus needed to be elsewhere, but she deserved an answer. Rose rubbed circles on his hand with her thumb. "Some things are fixed, some things are in flux. Pompeii is fixed."
"How do you know which is which?" Donna pressed.
The Doctor stopped and turned to her. "Because that's how I see the universe. Every waking second, I can see what is, what was, what could be, what must not. That's the burden of a Time Lord, Donna. And I'm the only one left." Rose stood on her tiptoes and pressed a kiss to his cheek, a silent reminder of "there's me."
Roaring echoed through the tunnels.
"They know we're here." Rose pointed out.
"Come on." The Doctor started walking again and the ladies followed. The tunnel let out to a large cavern populated by fully grown Pyroviles. "It's the heart of Vesuvius. We're right inside the mountain."
"There's tons of them." Donna gasped for air in the heat. The three of them ducked behind a rock to avoid being seen.
"What's that thing?" The Doctor pulled out a monocular and pointed it at something with a light inside on the far side of the cavern.
"Oh, you better hurry up and think of something. Rocky fall's on its way." Donna ordered.
"That's how they arrived. Or what's left of it. Escape pod? Prison ship? Gene bank?"
"Why the volcano?" Rose asked.
"Maybe it erupts, and they launch themselves back into space or something?" Donna suggested.
The Doctor shook his head in fear and resignation. "Oh, it's worse than that."
Rose closed her eyes against what she knew must be coming. The TARDIS brought and kept them here for a reason, and she knew the reason wasn't good.
Donna's eyes widened. "How could it be worse?" She looked up at as the noise around them got louder. "Doctor, it's getting closer."
"Look," Rose pointed to Lucius at the ridge on the other side of the cavern.
Lucius shouted, "Heathens defile us. They would desecrate your temple, my lord gods."
"Come on." The Doctor rose but stayed in a crouch position.
"We can't go in." Donna argued.
"Well, we can't go back." The Doctor started moving and the two women followed.
"Crush them. Burn them." Lucius ordered his gods, and a Pyrovile appeared in front of the time travelers. The Doctor squirted it with his water pistol, and the three of them took off running. "There is nowhere to run, Doctor, and daughters of London."
The travelers reached the remnant of the Pyrovillian ship. The Doctor stopped just outside of the pod and motioned for Rose and Donna to get in the pod. Neither obeyed, they refused to leave him.
"Now then, Lucius, my lords, Pyrovillian, don't get yourselves in a lather. In a lava?" He tilted his head at the Pyroviles and Lucius but received no laughter. "No?" He turned to Rose and Donna, but they just shook their heads at him. Rose smiled at him lovingly. He sighed, "No. But if I might beg the wisdom of the gods before we perish. Once this new race of creatures is complete, then what?"
Lucius answered for them, "My masters will follow the example of Rome itself. An almighty empire, bestriding the whole of civilization." He smirked, and Rose scoffed at his pride. How could he genuinely believe that he would be ruling alongside them if they succeeded?
"But if you've crashed, and you've got all this technology, why don't you just go home?" Donna asked, and the Doctor looked at her with pride.
Good, Rose thought. She had been worried that they would have issues after this trip. Rose could sense they needed Donna, and she wasn't ready to let their friend go.
"The Heaven of Pyrovillia is gone." Lucius answered. Rose's eyes turned gold, and the Doctor narrowed his eyes.
Donna flinched a little. "Why do your eyes do that whenever a planet goes missing?" She asked then blinked rapidly. "How did I ask that question?" Rose laughed, but she didn't have an answer for either question.
The Doctor turned his attention back to Lucius, "What do you mean, gone? Where's it gone?"
"It was taken. Pyrovillia is lost." Lucius sensed the Pyroviles growing weary of the topic.
"The stars are going out." Rose mumbled under her breath. The Doctor glanced at her quickly but decided that comment would have to wait.
"But there is heat enough in this world for a new species to rise." He spread his arms wide.
The Doctor scratched the back of his neck, "Yeah, I should warn you, it's seventy percent water out there."
Lucius narrowed his eyes at the Doctor and spoke condescendingly, "Water can boil. And everything will burn, Doctor."
"Then the whole planet is at stake. Thank you. That's all I needed to know. Donna, Rose." He gestured into the pod and turned to follow them inside. He locked the doors with his sonic screwdriver then started to examine the circuit boards again.