The Master woke up tied to a chair.
He looked around, processing almost instantly. Colorful lights, complex gears-TARDIS-the Doctor's TARDIS-had his plot really been going that poorly before he lost consciousness?-quick memory search: yes-horror, panic, fury, and, deep down, a thread of something utterly treacherous that he immediately suppressed with a shudder-"YOU CAN'T-" he started-
"Good morning! All better now, are we?" the Doctor shouted cheerfully, appearing from the other side of the controls. "I hope you got the tormenting-innocent-humans thing out of your system for a bit just now, because I won't be giving you any more of them. You know we've been here before, we've seen this room and walked this floor-isn't that a song? What song is it? Why don't I remember what song it is-"
"-This won't be like last time!" the Master interrupted angrily. "I've learned my lesson! I mean it! My lesson, that I taught myself, all those years ago when I almost succumbed to you-I'm never letting you in again!"
"Oh, is that the lesson you learned?" the Doctor said, frowning. "Because what I would have gotten out of it would've been something about not turning my back on you when you're armed and conscious, except I already knew that, as did everyone else with one or more neurons except yourself-"
"-You got so close to infecting me, to weighing me down-"
"-Oh, well, it doesn't change anything about what happens next," the Doctor said. "I'm keeping you here, for real this time, just like I said I would all those years ago."
"You can't!" the Master sputtered. "I'm not setting foot in that vault again!"
"There is no vault. There doesn't need to be-because I made this." The Doctor dived under the controls and reappeared with an-object-that resolved into a cluster of small black boxes connected to each other by a tangle of blue and white wires. Two long gray wires trailed out from the central cluster, ending in small spheres. The Doctor picked up one of the spheres and pressed it to his forehead, where it stuck.
"What is that?!" The Master felt a terrifying intuition looking at the boxes. They reminded him of-
"You have two options," the Doctor said, advancing on him with the sphere at the end of the other gray wire in his hand. The Master flinched. "Option one: you sit in that chair, and I stand here watching you sitting in that chair, for the rest of our lives. It'll be a contest. Which of us can endure more time with absolutely nothing and no one but each other for company? Which of us"-at this he grinned wickedly-"likes the other more?"
"No. NO!" the Master yelped, pressing as far back in his chair as he could, but the restraints were perfectly fitted, and he barely moved.
"Option two"-the Doctor held up the sphere in front of the Master's face-"you put this on. It'll create a permanent link between our brain cells. It's a virtual leash. You won't be able to move more than thirty meters away from me, and I'll feel any sudden or unexpected movements you make. The only complication is you have to want it. You have to consent. I borrowed the mechanism from some nasty monks a long time ago. Really quite awful, those creatures, but clever. Oh, so clever."
"That's ridiculous! I don't want it! I'll never want it!"
"We'll see about that. Remember option one." And with that, the Doctor stuck the second sphere to the Master's forehead.
The Master gasped. The sphere's psychic field inserted like a fishhook into his mind. It didn't hurt. It did far worse than hurt. It was fishing for the treacherous thing, the thing he had been suppressing, the thing that had gnawed quietly at him since he woke up. He fought the hook, pushing at it, trying to shake it off, but it found the treacherous thing and yanked it, shining too brightly to look at, to the surface.
"It worked!" the Doctor declared, triumphant, and pulled the spheres off both their foreheads while the Master gulped for air with shuddering breaths. He released the Master's restraints with a wave of his screwdriver, stowed the contraption of wires and boxes back under the TARDIS controls, and leaned eagerly on the control panel. The Master stumbled out of his seat, trying to get himself under control, catching the bright treacherous thing and shoving it under the dark covers where it belonged.
The Doctor flipped a switch seemingly at random, laughing madly. The TARDIS whirred. "Tell me, then," he said, "where shall we go first?"
"Hell," the Master snapped. He leaned on the controls on the opposite side of the Doctor, his breathing still hard.
"Of course!" The Doctor smiled with the radiance of three suns. "You told me all about Hell when you were Missy. Hell, the planet. A beautiful planet, named in irony. Great twisted bridges and arches of natural rock, leaping and dancing over a landscape of forest and lake and geyser and bloom. Long trails along the rock bridges, the view from them different with every step. But you only ever got a glimpse of it, and you always regretted not going back."
"That's not what I meant," the Master snarled, but they were already on their way.
They touched down at the head of one of the TARDIS guidebooks' most favored trails, a walkway of deep red rock that wound above a jumble of lush valleys carved out by natural stone walls hundreds of meters tall, climbing to the top of distant cliffs. They had landed at dawn. The trail loop would not return them until nighttime, when the powerful auroras in the sky above would shine to match the bioluminescent vegetation in the valleys below. The Master dreaded every bit of it.
"A psychic leash," he mused as they stepped out onto the red rock, trying to focus on anything other than the beauty of the landscape. "I can feel it. Like a rope growing out of my head. But there must be a way to cut it. All ropes can be cut. What would happen if I were in the TARDIS and you weren't? Would it refuse to leave? Or leave without me? Or would it drag you behind it all the way through the time vortex? What if you died? Would I have to carry your body with me forever? I suppose I could burn you and keep your ashes. Or is it simpler than that? Could I just eat you?"
"Look at the clouds," the Doctor said, ignoring him entirely. "I've never seen such orange clouds. Look at the trees! Look at what's covering the cliff-side over there! That's a network of branches from a single plant, climbing over hundreds upon hundreds of meters of rock, clinging to it for support, and the same network spreads even farther underground! What an excellent suggestion this planet was. I think I'll like traveling with you."
The Master glared at him. "The question is, how to kill you, now that you can see everything I do through the link? I would have to take a series of actions that are each perfectly ordinary on their own but add up to your inevitable downfall, with you suspecting nothing. Oh, but it's not just my actions that must be concealed-even my clearest thoughts leak through the link. So I would have to block a full understanding of my own plot even from my own mind. Confuse my own memory, but stick to the plan. What a delicious puzzle. I'm sure I can figure it out."
"There are entire species of small animals that live only on that single tree!" the Doctor said. "Also, the psychic link is only half the problem. The other half is that you only try to kill me when you know you won't succeed."
"That is not true!" the Master shrieked, but he couldn't think of a counterexample, so he didn't continue the argument.
They kept walking. The red rock path meandered one way and then another, exposing a different scene at the bottom of each little valley among the towers of stone-here a bubbling white lake like a pot of boiling milk, surrounded by thick vines trailing tentacles into the froth; there a vast patch of giant flowers-and the red dust stirred up by their feet had begun to color the Doctor's clothes and hair and face, rather like the red pollen on Gallifrey, which made him look so much-younger-
The Master cursed inwardly. The bright treacherous thing in his mind had started creeping out from its hiding place again. He kicked it back.
"On second thought," he said viciously, mostly to break the all-too-companionable silence, "I don't have to kill you myself. All I need to do is wait until you inevitably get yourself into trouble and then persuade your enemies to give me your body. Have you given any thought to how dragging me around will affect your little human-rescuing hobby? I'm not planning on helping next time, you know. I'm really not."
"Well, then," the Doctor replied dryly, "all you have to do is make friends with whichever of my enemies we run into next. There's only one problem with that-none of my enemies like you either."
"I could charm their socks off if I tried," the Master said defensively. "They're just not much use most of the time." He made a face. "Why do you do it, really? The rescuing-what's the point? Jumping into one of the trillions, quadrillions, of places and times where a few people are about to die, letting half of them die anyway, scooping up the other half so they can be killed by a slightly different monster at slightly different coordinates instead. Everyone dies, everything ends, everything hurts. You can't put off the hurt forever."
"Ah." The Doctor looked at the Master with a strange interest on his face. "That is how you think, isn't it. Nothing good can last, so chase it away before it goes. Destroy what is beautiful before it falls apart, debase what is great before it disappoints you. Joy is a trick the universe plays to enhance pain. Loneliness is the only protection against loss. That's your whole life, isn't it."
"I don't cling to denial like you."
"And yet you can't help but keep trying to fill the void. You fill it with things you own, things you've broken. They don't help, do they. They only make you lonelier."
The Master snorted. "And you're doing so much better you've resorted to dragging me around on a leash just to have a hiking partner. Speaking of which, I just realized. Silly me. I don't even need you to die, only to suffer. You act patient, but we both know very well how little it takes to push you over the edge. You'll get sick of me soon enough."
The Doctor smiled up at the sky. "Did I ever tell you," he said, "that these days I know so many languages so well that the TARDIS hardly ever bothers to translate for me? Do you know what that means? It means you're the only person from whom, when you speak, I hear Gallifreyan. It sounds beautiful."
"I hate you," the Master promptly said in English.
"I love you," the Doctor replied cheerfully, also in English.
"You're disgusting," the Master snapped, switching immediately back to Gallifreyan. The truth was that he was in the same boat as the Doctor. He had to spend enough time listening to filthy human tongues during his various human-related schemes. The last thing he needed was for the Doctor to torment him with one of them when nobody else in the easily accessible universe spoke the music of Gallifreyan.
"LOOK AT THOSE BIRDS!" the Doctor shouted, pointing at a faraway flock of creatures that actually looked more like dragons than birds. The Master rolled his eyes and lapsed back into sullen silence.
Oh, but it was beautiful. Thin rivers of lava winding lazily out of smoking vents, their destination a distant sea; great whirlwinds high up in the atmosphere that sent the orange clouds spinning like children playing; and the ever-present stone, towering as elegantly over the landscape as the palaces and bridges of the Time Lords. It was true, what the Master had told the Doctor: he had (as Missy) stopped here briefly, once, when he was on the run, and the sight of it had haunted him ever since. In the vault, he had temporarily put aside his fears and imagined returning, perhaps even with the Doctor, just like this. Now he was back to his normal state of affairs, and all he wanted to do was flee.
But there was nowhere to flee to, so he kept walking, his worst enemy and only friend beside him. The Doctor continued to chatter about inane things and he continued to dispatch them with a carefully-calculated mixture of silence and sarcasm. It was obnoxiously, oppressively comfortable. Comfortable like Gallifrey, like the vault. How could it be that he was only ever comfortable like this when he was in prison?
The bright treacherous thing stirred and swelled in its hiding place. The trail of red rock took them up and up, to the top of the cliffs that had loomed ahead of them at dawn, to the highest point in the region, so that now before them they could see-
-the rock structures falling away rapidly, followed by a strip of red sand, and then the sea, and floating on the sea from beach to horizon was an iridescent layer of microorganisms which made it look like the surface of a single enormous opaque soap bubble, and oh god but it was beautiful-
-the Doctor sighed contentedly and sat down on a natural rock bench nearby. The Master sat down next to him, closer than he really meant to, hardly aware of what he was doing. He felt unsteady, out of breath. He felt as if he'd been shackled to a powerful flying carpet and was fighting a losing battle to keep it from taking off.
"It's perfect, isn't it?" the Doctor said softly, placing his hand on the Master's back-
-and it really was too much. Red rock and orange clouds and shining, shining sea and, most unbearably of all, the love of a good man. The bright treacherous thing threw off its covers and roared and burst into silver stars and gushed out of his mouth as wild, hysterical laughter.
"What-"
"You're-right," the Master gasped. "About-me."
"I-"
"This is exactly-what I can't-take. What I can't stand."
"Master-"
"But it's no use"-the feral giggles continued to pour from his mouth-"escaping-because you always find me again. Because I need you to find me. Can't stand-not having this-either. Can't stand anything." At this point he discovered to his astonishment that, entirely without his noticing, his giggles had turned into sobs.
"Right," the Doctor whispered, and quietly drew the Master to him with his arms. The Master buried his face in the Doctor's shoulder.
"Everything-hurts," he mumbled.
"I know," the Doctor said, and now his voice was breaking too. And so they clung together on the cliffs above the sea and cried for the way the cliffs would crumble and the sea would evaporate and they would inevitably be separated again. And when they were done they dried their tears and gazed once more upon the iridescent waves.
"Let's take a boat out there tomorrow," the Doctor said.
"Let's see how fast I can sink it," the Master shot back, but he was smiling helplessly, and he knew he had lost. He knew also that later he would regret this, curse himself for surrendering, for flying too close to the Doctor's black hole again. Later, in a day or a year or a millennium, the first moment the Doctor's watchfulness slipped, he would run. He would run as far as he could and swear to himself that he'd stay away, only to find himself enslaving more humans or building more Cybermen or anything, anything to get the Doctor's attention again, and the cycle would repeat. Later.
Later. But for now, he relaxed into the arms of his worst and only friend and gave himself up to the treacherous thing, the unbearable thing-the deep, overwhelming, impossible, irresistible, awful, perfect happiness.