The Doctor had dematerialized the TARDIS the moment they'd entered the ship. "Too risky, hanging about," he'd said, as he'd flipped and switched and poked. "Either of them find a way into this ship, and it might prove disastrous."

"I thought the TARDIS was impregnable," Peri insisted.

"The three hell gods from this universe have powers that transcend our normal rules of reality," Seo — in her Ninth incarnation — explained. "They could force the TARDIS doors…" She clicked her fingers, "easy as that."

The Doctor snapped his head up to her. "You're certainly well informed," he observed.

Seo didn't say a word.

The TARDIS shook, and the Doctor struggled to steady it. "Old girl doesn't like time in this reality," the Doctor muttered. "Not what she's used to."

He managed to steady the TARDIS.

Then turned to Seo.

"Now," the Doctor said. "Before we head home… there's the question of what to do with you. And our little timeline problem."

Seo didn't answer.

"What are you going to do?" said Peri. "Erase your own memory?"

"I'm hoping," the Doctor said, "to avoid that particular situation." He gave a small huff, then muttered, "Where Time Lords are concerned, I always prefer to keep my memories. Just in case."

"Very wise," said Seo.

The Doctor studied her, carefully. It was clear, from his eyes, that his mind was still trying to work her out. Even if he knew he shouldn't. "You know the Time Lords, then?"

Seo didn't answer this.

"No, quite right, don't answer," the Doctor decided. "That's one thing going in our favor. So far, you've been quite discreet. Aside from a few…" He cleared his throat, awkwardly, "…emotions…" cleared it again, "…you've been silent about anything too damaging."

"I'm not mad enough to do something like that," Seo pointed out.

Adding, in her own mind — Not yet.

She still didn't understand what would cause her to go mad, in her next life. She knew it would happen. The truth was plain for any to see. She'd known she was doomed to go mad by her tenth incarnation for quite a while, now.

But she'd always assumed, by this point, she'd understand why.

Yet still. Nothing.

"So. Let's start at the beginning," said the Doctor, crossing over to her. "When I first met you, did I give any indication that I recognized you? Anything at all? Did you suspect I might be just acting like I didn't remember you, even though I'd seen you before? Or…"

"I don't think that'll be a problem," Seo cut in.

The Doctor paused. "You… don't?" he said. Then stubbornly stopped himself from trying to work it out. "You don't. Yes. I see. Well."

Peri looked between the two. Then, in a small voice, "You know, I think maybe… you two should have some time together. Just… to catch up."

Seo gave a little smile.

Yes. Seo could see it, now. The warrior queen she'd met on Krontep — the one who'd been so willing to trust her, had stuck up for her and fought for her, even when no one else would — that hadn't been just someone similar to this Peri. It had been the same person.

Now, here she was. With a younger Peri…

And a younger Doctor.

So many timelines Seo had crossed… so many things she wanted to say. And she couldn't say any of them.

No.

Focus, Seo!

She had to get a grip on herself. Collect her thoughts. This wasn't just a timeline mix-up, after all. This was all… some plot. She'd been sent here because of… because of… yes! Because of the Matrix! She'd been gathering fragments of the Gallifreyan Matrix. Had found a fragment which had… had informed her… that…

Except every time she tried to think about that, she'd catch another glimpse of her father. The way he looked at her, all curious and interested, like he was trying to work out a puzzle. So much like he'd done back when he'd been alive.

She'd forgotten just how much she'd missed him.

How big a hole was left in her life when he'd died forever.

How could she think clearly, when that grief kept pouring through her head?

Peri left the room.

And Seo couldn't help herself. Just ran over and swept her father into another hug. Not wanting to let him go. Not ever wanting to let him out of her sight again.

He was alive.

Oh, she just wanted him alive again! Wanted it more than anything!

The Doctor struggled to extricate himself from her embrace. "Now, really, this is getting us nowhere," he insisted. "You and I, young lady, need to have a serious chat about this current problem, and how we're going to solve it. That's difficult enough without you… constantly… embracing me."

Seo controlled herself. Stepped back.

"I… I understand," Seo said, trying to make sure her voice didn't shake. "You're right. I just…" Her lips broke into an involuntary smile, eyes watering up. "Seeing you again…"

"And that'll be enough of that," said the Doctor. "Now. Of the many things about this that are bothering me, one thing stands out most of all." His eyes narrowed. "You."

Seo shuffled. What had he worked out, already?

"You," the Doctor repeated. "You're clearly not in this universe by choice. Arrived without any vessel I can see. You were — if your reactions to my voice were any indication — not expecting me to be here at all. And yet… the improbability that the two of us would intersect, out of order, in another universe… well, it can't possibly be a coincidence."

"Agreed," Seo said. Shook her head. "But… you don't need to worry. I'm pretty sure I know who sent me here. And why. It's not your problem; it's mine. I'll make sure it stays that way."

The Doctor thought this over. "Well, I certainly hope so," he replied. "Because I was sent to this universe by the Time Lords. And — believe me — they do not act kindly towards those who meddle with the Laws of Time." He looked down at the TARDIS controls, irritated. "Last time it happened, I was put on trial. And I have no wish to do that again."

Seo froze.

As it all came together in her mind. "Trial," she repeated. "The Matrix. The trial!"

"I'm sorry?" said the Doctor. "You mean… the Matrix on Gallifrey? You know of such a thing?"

But Seo was thinking fast, now. "I thought it was my sister," she said. "Or me. But it's you! Oh, it makes sense — who sent me here, who sent you here! Why the emotional amplifiers were so strong, to try to make me accidentally give something away about your own future! Why Peri's here! We've all been manipulated — to get at you."

The Doctor was now looking more curious than ever. "Someone… is manipulating me?"

"But it won't happen," Seo decided. Staring into his eyes. "It can't. I won't let it."

"Won't let…?" the Doctor started.

He was interrupted by a crackle that resounded through the air. A crackle coming from the TARDIS central console, itself. A crackle that resolved itself into a faint voice.

The voice was unfamiliar.

But the touch of the mind that came with it… filtered through the ring around Seo's finger… was someone Seo could never forget.

The Doctor turned, his face growing even more curious. As he tried to unravel this latest mystery. But Seo wouldn't let him. This was his past, and it had to stay the same. She wouldn't let anything happen to him, not if it was her own fault.

"I'm sorry," Seo said.

The Doctor began to turn back to face her. But she'd already slid her hand into just the right position to give him a Gallifreyan sleeper-hold. And he passed out, in her arms.

Seo lay him down on the ground. Tapped a small kiss to his forehead.

"Never forgot you," Seo said. "Never will. Best hero the universe ever had."

Then she got up. Headed back to the central console, and began working at the controls frantically. Trying to finish what had begun — use the TARDIS to unscramble the multiversal communications ability within her ring, and establish proper contact.

There!

Got it.

"Jenny," said Seo, as the face blinked up onto the TARDIS scanner. She paused. Then realized. "Please tell me that's a new face. I've crossed too many timelines, today, already. I don't need to cross another."

"Sorry," said Jenny. "I'm from your future."

The Ninth Seo slowly let this absorb. Then narrowed her eyes. "You shouldn't be contacting me. Especially not using Father's ship. You're putting everyone in danger!"

"I had no choice," said Jenny. "Seo, you're already in danger. You've been dragged to that universe multiple times. In your past incarnations."

That was true enough.

Seo could feel the memories sliding into her mind. Creeping and crawling there, then lingering. New memories, from an altered past.

"The other incarnations have to get back," said Jenny. "And you're the only one who can do it. Your first self was traveling with your aunt, and I've brought her with me, to Earth, but—"

"Don't you dare," the Ninth Seo warned. Her voice low, bordering on vicious. "You know what could happen to her, if you use her to drag me back. I won't thank you for that; not in any incarnation."

"I wasn't planning on it," Jenny snapped. "I'm trying to find another way! And I think I know the answer."

"Enlighten me."

"You've intersected with Dad's timeline, when he was on a mission for the Time Lords," said Jenny. "Those Time Lords are going to make a tunnel for him, so he can get back here. Using the TARDIS, you can reactivate the rings on all your other selves. To let them all use that same tunnel."

The Ninth Seo froze. Stared at her sister.

"You want me to… what?!" she cried. "Cross that many timelines, in that many ways?! Are you mad?!" She leaned over the console. "Don't contact those Time Lords; contact ours! They might have their flaws, but they'll fix this. After all — I've been thrown into Father's past. And you know how the Time Lords are when people interfere with Father's past!"

"And when your Tenth Incarnation interferes with her own past, by bringing you there ten times?"

The Ninth Seo recalled all the memories that had grown inside her head, since she got here. Winced.

"Point taken," she muttered.

"Which means that we either use your aunt," said Jenny, "or you use my way of getting back. And no clever last-minute ideas, Seo — we don't want you wiping your own memory, or dying on the trip back home!"

Wiping her own…?

Seo froze. Suddenly staring, in horror, at the Doctor — her father — lying peacefully on the floor. Breathing. Alive. And she knew what would happen if… if…

Her hearts sank. As everything became clear to her. As the Ninth Seo knew what she had to do, next. What would result from it. And what it would mean for her next incarnation.

"Wiping my own memory," Ninth Seo repeated. "I'm not going to remember any of this, am I? Nothing about even entering this universe." She could see the future spiraling out before her, as she knew it had to go. And see how she'd get there. "This is how it happens. How I go mad. And I can't stop it."

"No, Seo, you're going to be fine!" Jenny insisted. "I've fixed it! You don't need to wipe your memory. You don't need to use the Key-part of yourself to return. You'll remember everything, and won't go mad! You'll…"

But Seo knew Jenny didn't understand.

And how could Seo tell her? What could Seo tell her? How much could Seo even manage to speak aloud, without losing her courage and chickening out?

"I'm sorry," said Seo. Cutting Jenny off. Eyes resting on the controls, as she fiddled with the TARDIS. "But this was always coming. It's what has to happen."

"Seo, what…?!" Jenny cried.

"I've used Father's TARDIS to unlock the rings from my other incarnations," said Seo. "Contact them. If I use the TARDIS telepathic circuits to boost my own mental signal, they can all latch onto my mind. That way, when I go home… they'll go home, too."

"What are you planning to do?" Jenny demanded. Now a little panicky. "Seo, what are you—?!"

But Seo cut off the communication between them.

No use delaying the inevitable.

"Courage, Seo," she told herself, getting to work. "You know… this is the right thing to do. The only thing left."