Later, Peri realised that Turlough had known before she had. Perhaps he'd seen it before, or recognised the urge to escape in her.
"Look after him won't you?" He smiled slightly, although his tone didn't quite match it. "He gets into the most terrible trouble."
The assumption in the words left her taken aback and mumbling, the Doctor stiff-backed and indignant.
"I..." Peri started hesitantly, but although Turlough smiled he turned away before she could manage more. After a moment, the Doctor spun round, all business again.
"Well, I should get you home."
"Oh must you?" Until the words were out, Peri didn't realise the depth of feeling in them. Couldn't put her finger on when she had decided somewhere inside, that was what she wanted. Something Turlough had already spotted and she'd missed.
The same as he'd known the slight tease in his parting words had more than a grain of real truth to them.
Peri recognised the Doctor's briskness as a covering up of emotion, after all, it was the third time in a few minutes she'd seen the same reaction. Kamelion's destruction has been the first and whatever had happened with the Master had left such an expression on the Doctor's face as he re-entered the TARDIS that he looked more as if he'd been newly bereaved than defeated an enemy.
Both had brushed off as quickly as he now brushed off her unthinking protest.
"Oh yes, your friends will be worried."
Peri followed him into the TARDIS, gathered her nerve for a moment as he tapped controls, then decided she had nothing to lose.
"It's funny," she began nervously. "Just before I met you I was saying I wanted to travel." She hesitated, unable to gauge any reaction from the Doctor, who had gone almost motionless in front of the controls. She assumed he was listening if only because he was no longer flicking switches.
"I've still got three months of my vacation left..." Hope wavered in her voice because the Doctor was so still and his face so closed. Abruptly, Peri felt like an interloper. How long had Kamelion and Turlough travelled with him? Here she was in the minutes after he'd lost two friends – been forced to destroy one of them – asking for a ride-along as it it were a school outing. No wonder he looked so pained at the idea.
Something like a sigh was the first sign of reaction to her words. He looked at her at last.
"And you want to travel with me?"
It was barely a question. His voice had lost the brisk cheerfulness, sounded almost resigned, as though he'd been waiting for the request, and not with any great pleasure.
Peri seized on it anyway, letting her eagerness show, as if her own enthusiasm could persuade him, cheer him, somehow re-conjure the quick, happy energy that she'd glimpsed before and that had been the only highlight of the day's bizarre adventure.
"Is that an invitation?" she asked.
At least he met her eyes this time, even as he brushed past her around to the other side of the console, tapping again at buttons and switches. Voice still flat, humourless.
"Actually it was a question."
Peri swallowed. Well if he wanted an outright request...
"May I?"
The sigh was clearly audible this time, but when the Doctor spoke again his voice was warmer, his face more animated.
"Three months you say?" He raised his eyebrows, rolled his eyes in her direction without quite looking straight at her. An amused, skeptical gesture.
"That's right," said, resisting the urge to cross her fingers, but hoping...
A sudden quick smile lit the Doctor's face and Peri felt a grin spread across her own as he threw a switch with such enthusiasm it seemed like an answer in itself.
"Alright. Why not?"
Whatever the switch had been meant to do, the actual effect was an appalling groan of distress that seemed to come right through the floor and an almighty lurch that catapulted Peri face first into the console.
She clung on, trying to keep her grabbing fingers clear of the myriad buttons, as the Doctor, whose hands had lashed out for a firmer grip as if by instinct, looked up.
His face was wry, wide eyed, but resigned rather than alarmed and he glanced across at her from his doubled over posture.
"Welcome aboard, Peri."
He looked up at the complex, coloured column which moved up and down in the centre of the column, the motion at present decidedly less than smooth.
"Sorry about the takeoff, the old girl does have her foibles."
Peri blinked and straightened as the motion of the column steadied.
"Old girl?" Perhaps it was nerves, relief at the day's near escapes, delight at the Doctor's agreement to her joining him and now the sudden adrenalin, but the urge to giggle was suddenly overwhelming.
The Doctor pushed himself away from the console and snatched his hands behind his back, the affronted dignity only making Peri giggle harder.
"Sorry," Peri restrained herself, still smiling.
"Hmm." The Doctor glanced at the central column again. "Well we're away now." He reached forward for a control and a the panel on the wall covering the viewscreen he'd used earlier slid upwards. "And there goes the Trion ship, safely off too."
Peri looked at the view, the planet rotating serenely below, the volcano not even visible from here, and the ship arching away, the metal catching the sunlight briefly before it disappeared.
The Doctor watched for several minutes after it had disappeared, until Peri moved to stand at his elbow.
"Did- Had you been travelling together long?"
The Doctor looked startled by the question. "What? Turlough? Oh... longer than he initially intended, I dare say." He smiled. "Not really a natural adventurer was Turlough. Tegan either for that matter but they both-"
He stopped abruptly. Turned from the screen and tapped a button which lowered the panel, hiding the view and leaving Peri looking at his back again.
"Well, they're both on their way home now. Where they wanted to be."
His fingers strayed idly over the controls for a few seconds, touching but not pressing switches and sliders. When he turned back to Peri he was smiling again and his tone was light.
"I suppose I should show you around shouldn't I?" He gestured at a door which Peri vaguely remembered leading deeper into the ship. "The TARDIS interior can be a bit confusing but I'm sure you'll soon get used to it. Inasmuch as that's possible with variable-geometry dimensions of course."
He strode ahead but stopped before he reached the door and spun round. Another flicker-fast change of mood had drawn a slightly puzzled, slightly worried, strangely apologetic little frown across his face.
"Peri... Why are you here?"
She stopped dead in her tracks, alarm stricken that he was about to turn her out after all, but he shook his head, raised his hand in reassurance at her expression.
"I've already said you can come, but I want... I need to know why." He sighed. "Turlough never intended to stay, not really. I was a means to an end. At first anyway. Later things changed but he would always have left. Tegan... did not leave happily." He hesitated for a split second before continung. "And that was my fault. Today was not atypical I'm sorry to say, and Tegan saw that too often and I never did see it in time."
He met her eyes steadily though his voice sounded as though he was steeling himself to go on, forcing the words out.
"Nyssa's planet I could do even less for than Sarn, she came with me while her world died. She made her own choice to leave, eventually. A brave choice, a worthy one, but not one I'd have wanted for her, not a safe place I'd have chosen to leave her. And Adric..."
His gaze faltered but held hers. "Adric died. He died on a spacecraft I took him to and I left him on, trying to save a world that wasn't his and I couldn't save him. As I couldn't save your new friend Kamelion. As I couldn't stop with Master without..." He paused. "Inaction is action itself sometimes. I killed him too, in every way that matters."
He gave a sad, bitter little smile.
"Turlough may have been joking but he was only half right. I don't just get myself into trouble I get everyone around me into it too. And while I always seem to walk away, sometimes they don't. Even here. If I hadn't packed the Master off to Xeriphas, feeling oh-so-clever and pleased with myself at having dodged the need to deal with him permanently – again – then he'd never have found Kamelion, never been able to bring us here, or meddle with the volcano and drive all those people from their home."
Peri found herself lining up counterarguments without even thinking but before she could open her mouth to try any of them, the Doctor had carried on.
"So what in the all the worlds did you see today to make you want to travel with me?"
Peri hesitated.
"I can still take you home you know." The Doctor's voice was calm, no longer cold or full of angry frustration. There was no challenge in it. Peri rather suspected he'd be relieved to have her say yes.
"Anyone would think you were trying to talk me out of it..." she tried, voice wobbly knowing the attempt to lighten the mood would fail even as the words left her. Habit. Silly childish habit.
"Peri,.."
Peri reached into her shorts pocket a drew out a slim notebook,
"There's not one thing," she said, "Not really. But look."
She opened the notebook carefully peeling the centre pages apart.
The Doctor moved away from the door, his expression changing to puzzlement as he looked down at the book, at the flower she'd pressed there.
Peri looked at it again too. The six flattened silver-white petals formed a soft edged triangle, framing a vivid golden throat from which a deep red stamen protruded.
"I've never seen one before," Peri said, "Because there aren't any on Earth are there?"
"No," the Doctor said. "I'd say it's a native plant, possibly even specific to the area of the settlement, where the soil chemistry is affected by the volcano."
He looked up from the plant, an odd sort of smile on his lips.
"And that's why you wanted to come with me? Alien flowers?"
"New flowers! New... Everything." Peri was talking quickly now, thinking out loud as much as she was explaining to the Doctor. "I thought college would be new, different, but I've been sat there learning the same thing that everyone else has learned before me for a hundred years! I want..." She flapped her hand and dropped her gaze back to the book, words running out on her. "Oh I don't know. Something."
"To see another sky."
Peri snapped her head back up to find the Doctor watching her, the skepticism on his face replaced by another unreadable expression.
"Yes," Peri put the book back in her pocket. "I suppose so."
The Doctor smiled. "Well, who am I to argue with that ambition? Come on, I was showing you around wasn't I? The TARDIS library should be able to tell you the name of your alien crocus, we'll start there shall we?"