Picking up her satchel from where she'd left it by the hatstand, Rose followed Tegan and Nyssa. The Doctor had disappeared from the console room directly after piloting the TARDIS into the vortex. "Where are we going?"

Tegan cracked a smile, but it was Nyssa who answered. "To celebrate. We survived."

Rose thought they meant alcohol, or maybe some alien equivalent, but instead they went to the kitchen, and snagged several colourful bottles of vintage soda from the fridge. The fridge, unsurprisingly, given the interior of the TARDIS, was bigger on the inside. Rose picked out a red bottle of cherry soda, shuddering as her hand brushed a bottle exactly the same colour as the strange lightning. "Is it really vintage?"

Tegan shrugged easily. "Not the faintest. Knowing the Doctor, there's a fifty fifty chance either way."

They all sat down at the large laminate table occupying a good chunk of the space. Rose raised her bottle of cherry soda. "To survival and thwarted invasions."

They clinked their bottles together, echoing the sentiment. Rose took a long pull of her soda, before setting it down on the table. It tasted tangier than she'd expected. "So how did you guys end up travelling with the Doctor?"

Tegan tipped her chair onto two legs, her face going blank as if remembering a memory not entirely pleasant. "I was with my aunt Vanessa, driving me to the airport for my first day as an air stewardess. Our car broke down, and I went to go make a call in what I thought was a police box. It turned out to be the TARDIS, and I got lost."

She let out a laugh that was half-rueful, half-irritated, and tipped her chair back down. "The Doctor keeps trying to get me home, but he hasn't managed yet. Someday he will, but until then, here I stay."

Tegan shrugged, and looked at Nyssa. Rose privately wondered if the Doctor's driving skills were really that bad, but kept it to herself.

Nyssa took a deep drink of her soda(a green permutation oddly called Cel-ray), almost as if thinking of a possible answer. Then she set the bottle down. "I asked the Doctor for help with a problem."

Almost as an afterthought, she added, "He was very different back then."

Well, if that wasn't an evasive wording, Rose didn't know what was. Secretly, she resolved to ask the Doctor. Changing the subject, Rose asked, "What's with the celery soda? There has to be a story behind that."

Nyssa and Tegan both got glints of mischief in their eyes. Tegan grinned slyly, and leaned toward Rose with a conspiratorial air. "You see, the Doctor hates celery, and the TARDIS likes to play pranks. So this one time, we landed in New York, and when he went out, we lugged a case of the soda back in. Naturally, the TARDIS hid the rest of the soda when he came looking for a bottle."

Nyssa burst into helpless laughter, slapping a hand down on the table for emphasis. "When I came in, he was just standing there, staring at the fridge, and I asked him if he needed something, then the Doctor just looked at me reprovingly, and said 'you know what you did.'"

Pretty soon all three of them were in gales of further laughter. Eventually the storytelling turned to past adventures and old friends, including Adric. "-and so I called him Pyjama Boy! Adric was not amused, to say the least."

Rose looked between her two friends, reluctant to shatter the happiness they were feeling. But she felt that there was something crucial she was missing, something vitally important. Slowly, hesitantly, she asked, "How did Adric die?"

Tegan's face immediately grew stormy with rage, and tears ran silently from Nyssa's eyes to spatter like broken glass on the table. Rose felt instantly horrible for prompting her friend's pain, but she was spared changing the subject by Tegan beginning to speak in a flat, angry voice. "We were chasing cybermen, and we landed on a freighter crawling with them. Long story short, they'd turned the freighter into a massive bomb, and launched it at the earth. The cybermen captured me, and used my life as a bargaining chip. The Doctor agreed to save my life in exchange for Adric staying behind while he brought the cybermen onto the TARDIS."

A volatile mixture of sorrow, white-hot rage, and aching pity was churning in Rose's gut.

Tegan continued on, seemingly oblivious to the battle raging within Rose. "The Doctor tried to pilot the TARDIS back to save Adric, but some cybermen shot up the console before he could. The freighter exploded, and Adric died. But the TARDIS is a time machine. He could save Adric any day he wanted."

The wave of rage crested, taking ahold of Rose's brain. Rose shot to her feet, knocking over the red vinyl chair. "I'm gonna go give the Doctor a piece of my mind."

Tegan and Nyssa stared at her in alarm. At last, Nyssa spoke. "How are you going to find him?"

Rose smiled grimly. "I'll manage." She strode out of the room.

Fifteen minutes later, Rose stormed into the beautifully green atrium that Nyssa had called the Cloister Room. The Doctor sat cross legged on the other side of a tranquil fishpond with several fat koi swimming in it. His eyes were closed, and he was completely moveless. Until Rose stopped across from him, her arms folded across her chest, glaring daggers at him. The Doctor slowly opened his eyes, and gazed at Rose. His pale blue eyes held no reproach or anger. Rose, however, had anger aplenty. "Adric. Explain."

Now emotion entered into the Doctor's eyes. Vicious, creeping guilt, and potent sorrow. "I couldn't save him. I still can't. As a time traveler, there are some things you simply cannot alter without devastating consequences."

Rose sat down across the pond, and gestured for him to continue.

He did, blue eyes puzzled and showing the beginnings of intrigue. "Picture, if you will, a house. Some things, like picture frames and knickknacks, can be moved without any problems or great changes to the house. Those are your mutable events. Then you have larger objects like furniture and non-loadbearing walls. Those are your pivotal events. And finally, you have loadbearing walls, which if you mess with them, the entire house will collapse. Those are your fixed points."

Rose's rage was fading, as things began to make sense. "So if you change a mutable event, not much changes. If you change a pivotal event, history is significantly different. What happens if you change a fixed point?"

The Doctor cracked a wan smile, as if he thought she was paying attention. "Then the entire universe collapses."

Rose gaped at him. "Pull the other one, why don't you?"

But the Doctor's expression was deadly serious. "There's a reason that the only species with the natural ability to time travel has the ability to see Time, including fixed points."

Rose was starting to believe him. She looked at the Doctor curiously. "Your species?"

He smiled tiredly, shifting to lean against the tree behind him. "I'm a Time Lord."

Rose grinned cheekily, her tongue poking out between her teeth. "Right, because that isn't pompous at all."

That startled a laugh out of the Doctor, and Rose paused to savour the sound. Then the Doctor met Rose's eyes, and his expression was earnest and sad. "I would save Adric if I could, but I can't. I'm so sorry."

His eyes glittered with unshed tears. For some reason, Rose couldn't take seeing him in pain. She stood up, rounding the fishpond, and sat down beside him, leaning into him. After a moment, his arm wrapped around her shoulders. Rose looked up at him. "For what it's worth, I'm sorry too. Sorry I yelled at you, sorry you lost a friend, and sorry you had to choose between Tegan and Adric."

She dropped her gaze again, playing with the hem of her jumper. "Can I stay and talk a little while?"

The Doctor smiled softly at her. "Of course you can."