O was all the things he couldn't be.

First he was a colleague. He replaced the real O with such silent ease he almost felt sorry for the stupid humans. And then he bided his time.

He knew the Doctor would be honorary head of their intelligence, so all he had to do was outperform the other agents in his intelligence role and make no secret of his beliefs in alien interference and he'd be introduced eventually.

It happened sooner rather than later; C set up a meeting and couldn't attend himself, leaving the two of them alone.

He watched from the room above as the TARDIS landed and a lone woman stepped out. So she was female this time, blond and cheerful.

God, he couldn't wait to mess with her.

He watched as she stuck her hands in the pockets of her long coat - some things never changed - and sauntered into the building like she was just walking into a cafe and not an intelligence agency. A slow grin spread over his face and he stood, pacing the room. He could hardly bring himself to keep still.

It took everything he had not to clap his hands as he watched the lift light come on, climbing the floors until it reached its destination.

The doors slid open, and there she was - blond hair, bright eyes, bright smile, bright blue sky coat. She was the polar opposite of her last incarnation - young and vibrant, wearing a rainbow shirt with no collar...

"Hi!" she said, beaming. Yorkshire accent, he noted, making a mental note to adapt his own to match. Familiarity always bred positive feelings - trust. "I'm the Doctor. O, isn't it?"

And she approached, reaching out her hand. He took it. He was so sure he would giggle with delight if he made a noise that he couldn't get a sound out. He stared at her, stammering.

"C- can I have your number?" he said. She blinked, surprised.

Had none of the Earth males asked her that yet? Maybe there was a benefit to looking like a tongue-tied idiot, because she didn't actually look insulted. Just curious.

"Sorry," he said quickly. "Big, big fan. Everyone here says the Earth would have been cooked a long time ago if you hadn't masterminded all those plans to stop them."

"Oh - well, I had help. UNIT, Torchwood..." She smiled. "Smart people like you..."

They were still holding hands. She noticed the same time he did, and let go.

"So," she said, smiling. "Looking forward to saving the earth with you."

"Yeah," he said, voice breathy as he struggled to contain his excitement. "Me, too."

- -

Second he was a confidant.

It happened gradually, with him shyly texting the Doctor an opening salvo and her responding with cheerful over-enthusiasm. Soon they were texting regularly, even about trivial things. He invented things for O to be worried about and she would console him, advise him, joke with him.

Several times he caught himself smiling or laughing at her texts. The Doctor was charismatic as ever, he noted. It was so easy to be taken in by her...

But the plan continued on. He began to get everything into place, making contact with Barton, acquiring the Silver Lady. All he needed to do until the trap was ready to be sprung was keep up his human disguise.

He put up with socials. Led a double double life as a normal man when he deigned to try dating. How the hell the Doctor had fallen in love with (married, even) human beings, he just didn't know.

The nature of her texts changed, got more intimate. Occasionally she would let slip something that worried her. Something that had hurt her. He got to be the one advising her.

The nostalgia was uncanny. It took him right back to their Academy days. They knew everything about each other, then. It was funny, comforting almost, how easily it came back to him.

Careful. He had to be careful.

One day he was called in to speak to C.

"Is there a problem?" he asked.

"Not at all. I just wanted to congratulate you on your-"

His phone pinged suddenly and the Master pushed down the urge to check who the message was from. "Apologies," he said, switching it off. "Should've put it on silent."

C chuckled. "Another of your women?"

"Excuse me?"

"The others mentioned you've been dating lately." C smiled a superior smile. "It sounds like you have a type."

The Master's neck prickled. "I don't know what you're talking about."

"Really? They said you have a thing for blondes." He chuckled. "And over achievers, too. Like them smart, I suppose?"

The Master fumed. A human with a doctorate was a minimum requirement for making his "dates" tolerable. It didn't make them smart. But he bit his tongue and laughed like they were just having a joke.

A few days later, he requested a transfer to the deepest outback.

He'd had quite enough of human company to last him at least a hundred years.

- -

It happened without fanfare.

She called him a friend.

Over text, but still:

You should meet my other friends sometime!

"Other". Like he was one, too. He contained himself, typed out his response:

Love to. And to see you again.

If she read between the lines, the meaning was clear:

I'd love to see you again (not your friends).

His phone pinged, a simple smile emoji response.

She never had been good at reading between the lines when she wanted to trust someone.

Or maybe she knew. Maybe she was just ignoring what she should sense deep down, because she wanted him to be good. And she needed someone like O. A smart secret agent. An intellectual equal amongst her friends.

A few days later, the most explosive message yet.

"Text us your location. Kisses."

The Master breathed in deeply, slowly.

Be careful.

He sent her back a coded response, then grabbed his chair to go wait outside for her. She was sure to crack his puzzle in no time.

Stick to the plan, he reminded himself, as the familiar blue box vworped into view.

Then she stepped out with a luminous smile.

He rose to meet her.

Finally, a companion. He made her and her human hanger-on tea and she nosed around his house while they talked.

It was hard, so hard to contain his excitement, so he channelled it back into his fanboy persona.

Little things seeped out of the cracks, though: he couldn't contain his annoyance at the old man's continued comments from the peanut gallery.

Couldn't she at least have chosen someone smart to bring along?

But then, when the Kasaavin began its push for freedom, the Master found his body moving of its volition.

To her. Guarding her, protecting her.

She didn't notice, too busy fixating on the sudden appearance of her friend, but he did. Cold sweats broke out on his skin.

This companion playacting was dangerous. He had to be careful. He had to get back on track.

The opportunity fell into his lap when he had to talk to the old man. He asked, casually as possible, what they knew about the Doctor.

It became obvious right away: absolutely nothing. For whatever reason, she hadn't trusted them with a damned thing.

He could scarcely hold in his glee. He'd been spending some of his interminable exile in the outback looking into what she'd be getting up to in his absence. Some of it good, some of it terror inducing. And going by the look on the old man's face, it was going to be fun enlightening him...

She interrupted then, an abominable iced tea mix in her hands. Oh, well. Next time.

His mask slipped again when she was decoding the message on the porch. She keyed it into languages at the end of the known universe and the Master couldn't resist looking at Yaz with a 'are you appreciating how smart she is?' expression.

He didn't think Yaz did.

- -

"I read your file," she said, because of course she had. "You were a champion sprinter."

A dozen lies went through his head, but nothing she'd easily believe. He hesitated, drawing the moment out. But then, no.

He wanted her reaction, pure and simple. "I did say look for the spy... Master."

She flinches back, eyes going wide.

"Hi," he said, grinning. He turned to the companions to brag, twist the knife that bit deeper how little they know her compared to how well he did.

He turned back, eager to see her response.

She had one hand over her mouth like she was going to be sick. Her whole posture was closing up with revulsion, even fear. He'd got what he wanted, a candid look at how she saw him, how the Doctor truly felt about him.

The Master's eyes narrowed.

It hit him then that there was something else O could be that he never would.

Loved.