Ever since she could remember, the most important thing to Ros Myers had been staying in control; hiding behind cold, shuttered eyes and keeping the world at bay. She didn't break down, or let emotions show; she made few mistakes and she learnt from them fast. She kept people at a distant, she knew how to manipulate them and she was one of the best at what she did.

Keeping herself emotionally closed off from the world had leant her strength, a process she had started after her mother left, and she had learnt that if you didn't get close, didn't trust other people then no-one could hurt you. You could be strong.

She'd had her rules and, with only one exception, she'd stuck to them, stayed protected, and so survived seeing and experiencing things that would have broken most other people. She was a master at denial and manipulating emotions – particularly her own.

Everything had been working fine, her guard had been impenetrable and firmly in place – perhaps she couldn't say she was happy, but in the world she had created for herself everything remained grey; you didn't get the white but you also avoided the black. She was safe.

And then she met Adam Carter, and that was the day everything changed. It was fine at first, she started the honey trap process as required, and apart from abstractly registering that he was handsome, she had remained cold, calculating. It had been easy to get his finger prints from the wine glass and the list of locations from his laptop – and now when she looked back she could see it had been too easy, Adam had been too accommodating, nowhere near as careful as an MI5 agent was expected to be, and perhaps the fact that this had slipped her by had been a sign. But she hadn't picked up on it. Not then.

The next time they met, he was angry, furious even and his blue eyes met hers, hard and cold. She didn't particularly care what he thought of her, in the current situation he was the enemy, but then he accused her of deliberately manipulating him by wearing his dead wife's perfume, and for some unidentifiable reason that disturbed her. She had previously thought that she was prepared to do almost anything to get results from people MI6 were working against, but something about imitating someone's dead wife struck a chord. She told herself she didn't care what Adam Carter thought, yet at the same time, she didn't want him to think she would stoop that low, that she was that cold, and much against her better judgement, she found herself protesting, telling him that she had worn that perfume since her sixteenth birthday, and something inside her was desperate for him to believe it. Afterwards she was furious with herself. He was just another agent, just another man with an idealistic view of the world, working to try and protect democracy, a system with so many flaws it was a wonder the country hadn't tumbled long ago, and she had ended up defending herself, trying to justifyherself to him, something she had sworn she would never do for anyone.

She had thought that was just a crack in her defence, something that time would smooth out and paper over, but then the entire fiasco with her father blew wide open, and she learnt that he had been prepared to kill two entire plane loads of innocent civilians, in addition to that MI5 agent, in order to achieve the goal. Anything to get a result, anything to get a result; that had been her mantra. But not wearing a dead wife's perfume and not deliberately killing hundreds of innocent people either. Perhaps that was the day when she learnt that there are limits to everything and that sometimes the 'greater good' just isn't quite worth it.

It was probably an important lesson, but that was still the day that she lost her father, the one person who she had trusted and loved, and the one person on whom she had modelled her entire system of survival. She had told herself that it still didn't matter, he might be her father, but he had been planning a mass murder, and she couldn't possibly love a man like that. She tried to shut it out for the remainder of the operation, but then when she got the call to go and meet Adam on the bridge and the realisation her father would go to jail hit, she discovered that she could tell herself he didn't matter all she wanted, but somewhere inside her shields there was still a little girl who idolised her daddy, and it was that girl who allowed her to accept the job from a man she had told herself was weak, to cry in front of him, and to show a much despised moment of weakness.

On her first day at the Grid, the members of the team looked at her with suspicion and dislike in their eyes and she returned it all blow for blow, knowing she was strong now. And when Adam approached her, she told him as much, informing him in no uncertain terms that she was not going to break down and that the moment on the bridge had just been a momentary lapse. He nodded, seeming to accept what she was saying, and backed off, and she firmly executed the tiny part of her that was pleased for his concern.

She suspected from day one that Malcolm would possibly never like her, her people had killed his best friend and it was a grudge that he could not forgive. She found herself hating him a tiny bit in return for this, hating his weakness, hating the fact that he was hurting because he had let someone get too close and then it had broken him. But mostly she hated that despite that weakness, she could see that Malcolm was strong, possibly even stronger than her, because he was dealing with his demons, facing them, afraid but not cowardly. She had never faced her demons, had been unable to and looking at Malcolm made her fear that perhaps that made her a coward. She hated him for that.

After a couple of operations, Ros could sense respect for her from some members of the team, respect for her abilities and her strength, begrudging from Malcolm but still there. But she never even got a hint of that from Jo. Admiration yes, but not respect, and after the debacle with Leigh Bennet, that disappeared, to be replaced with distrust and dislike. And so she found herself hating Jo a tiny bit too. Because Jo apparently thought that her strength, her coldness, was in fact not strength at all but weakness. Ros would never normally have even questioned herself because of what a colleague thought, but for some reason, here there was doubt, because Jo was obviously important to the team. Ros would never normally have questioned because before she would have understood, but she could not understand Jo. She was not a particularly good agent, she was weak, and yet she seemed truly valued by the other members of the team, by Zaf in particular. Jo was innocent, soft, and so completely human and yet the others didn't seem to see that as weakness, possibly even as strength. And Ros hated her for that.

Over the first weeks, she analysed everyone, Malcolm, Jo, Zaf, Ruth, Harry. In each of them there was something for her to hate; Malcolm facing his demons without fear, Jo for seeing strength as weakness, Zaf for being so obviously soft on both Jo and Adam and Ruth with her gentle eyes, inability as a field agent, and blatant love for Harry. Harry was slightly more difficult, because he was stronger than all of them put together, and she admired him for that, he lead them and she couldn't hate him, couldn't. His soft spot for Ruth was glaringly obvious even to an outsider and Ros suspected that if something happened to Ruth, Harry might break. She hated him for that. But then Ruth did leave, left the force to save Harry, and Harry didn't break, he remained strong, remained the leader, and that made it impossible to hate him. So she hated herself for not being able to hate him, and in turn that made her able to hate him. Just a tiny bit, but it was there. That little seed of hatred that would keep Harry out.

Adam was the worst of them all. He was so clearly the backbone, the rock of the team, and yet the rock was riddled with holes. His wife's death, his worry for his son, his breakdowns, his affair with Jenny. Ros tried to despise him for all of that, but she couldn't. Not even a tiny bit. Hating him seemed impossible, which was an impossible situation in itself, because he was worse than everyone. He had demons like Malcolm, but he couldn't face them, he was weak like Jo, but he couldn't acknowledge it, and he still had weak areas, like Zaf and Ruth and Harry, but his weak spot was a wife, his dead wife. She tried and tried, but she couldn't bring herself to feel even a tiny spark of hatred for Adam Carter.

Operations came and went, Armageddon's were prevented, and much against her will, she began to suspect that maybe, just maybe, she had found her place in the world. The team were not her friends, but they weren't just her colleagues either, they were the other essential pieces of a jigsaw puzzle and she was part of it too. The pieces couldn't see each other, they knew nothing about each other, but they somehow fitted, and they held each other together. It was a link that went below her barriers but it was still somehow impersonal so most of the time Ros could ignore it and pretend it wasn't there.

Impersonal vanished forever the day she was stuck on the Thames Barrier. At first it was just her and she was convinced she was going to die, obliterated beneath a six metre wall of water, not a sign of her left. She had been terrified, because dying in that way, along with a good half of London, would mean that she wouldn't have left a mark, not even a scratch on the surface of the world. The idea of such insignificance terrified her. But then Adam came, and she was so relieved to see him and she knew she shouldn't be, but she was and there was no getting away from it. She made some smart comment, and he replied with a quip about her not trusting him, which he didn't seem to realise was entirely true. Of course she didn't trust him, she didn't trust anyone.

And when the water came, Ros knew with a certainty that she was going to die, both of them were. And that certainty caused all her walls to come tumbling down, something so unexpected and terrifying and new that she became just a mess of emotions. She was really feeling things for the first time in years, she couldn't block anything out, she was just a helpless victim to the tirade of emotions. And she was terrified, both of them were, they screamed for help, the begging note in both of their voices completely undisguised and all she could think was 'No. No. Don't let me die. Not here. Not yet. Not like this.' And another part of her, smaller than the part that was desperate for her not to die, but still definitely there, was equally desperate for Adam not to die, wanted to get him out, felt responsible for him being there. She tried to fight it, fight everything, fight death, but she couldn't, because she wasn't strong enough. Adam kept going longer than her, rattling the grid above and with the growing darkness came the realisation that perhaps she couldn't hate him because he was the weakest of them all and that made him the strongest.

And then he had to be strong for her, pulling her back towards him when she was starting to drift, cradling her face in his hands in a startling gesture of intimacy, and she let herself cling to him in turn, fisting her hands in the front of his shirt, and clinging, refusing to let go, even when they finally burst through the grid and made it to the air at the surface. As she lay there, gasping, disorientated, everything spinning and the world too bright, she clung to him for security, as though he was just as important to her survival as the new oxygen ripping through her cramping lungs. She passed out then, the adrenaline overcoming her systems and perhaps he did too, she can't remember and she never thought to ask.

But when she woke up she was in the medical room at the Grid, safe, and alive but still feeling scarily vulnerable. She instantly started re-erecting her barriers, making sure that not an ounce of the fear or vulnerability she felt made it onto her face, and as she shut out the memory of how she had acted, of how she had, for a few brief minutes, let herself rely totally on someone else to save her, the wash of humiliation and shame receded as well, and eventually she felt that she could face Adam again without feeling that he saw her as something broken. She was back in control. And she had been able to kid herself that he was too, that the neediness that he had shown, he would simply forget, because it hadn't been her he was relying on, it hadn't been Ros, it had just been the only other source of human life in a horrible situation.

The feeling of strength and control had lasted all the way up until she had walked through the pods onto the Grid for the debriefing. It had lasted until she next laid eyes on Adam and when he immediately started towards her and she could see that he wasn't going to forget what had happened, wasn't going to just dismiss it. She had put her barriers back up but somehow they weren't quite the same, and she blamed him for that. She still couldn't hate him, but she blamed him.

But then unfortunately, even she, the master of deceit couldn't blame Adam for her letting him hug her, letting him deal with the debriefing while she sat in silence, for the inescapable, inexplicable urge that had gripped her to be close to him, just to touch him, to make her feel safe. She couldn't blame him for escorting her home, checking her security to make sure she would be fine, and it was definitely only her fault when she fell into his arms to let herself escape for a while, to hide from mental worry and trauma and just to feel, if only for the one night.

And when she woke up the next morning, to the whiny beep of the alarm clock, his arms were around her, and his arms were warm. He had rolled over and got up straight away, perhaps sensing that she couldn't deal with any other intimacy, but he tugged on her foot to wake her up, in a gesture that was friendly but felt frighteningly natural. And then later, when they were dressed and eating breakfast, keeping an eye on the news, as had always been custom for both of them, she had moved to the sideboard to wash up the few dishes, and he had come up behind her, wound his arm around her waist, and kissed the side of her neck, placing open mouthed kisses in a trail, from the sensitive skin behind her ears to the juncture where her neck met her collarbone. She had had to firmly suppress a moan, and the urge to tilt her head and give him more access, suppress the urge to let this go the same way it had the night before, and then he had pulled her back against him, into full contact with his body, and whispered 'I'll see you at work' into her ear. She had remained frozen in place for several minutes, even after she had heard the door swing shut behind him, and then had gone to sit at the table, hot and shaky. That was the first major crack in her new defence.

After that, it seemed that everything Adam did caused more of her barriers to crumble, and the urge to just open up and let him in was becoming ever increasingly strong, especially when he stood closer than was appropriate when he talked to her, covered for her without question, especially when there was a note of something she could not, would not name in his voice when he told her to 'take care' and when she sometimes caught him looking at her intently, a hint of a smile curling at the edge of his lips, he blue eyes alive and burning, as though they could see into her soul.

He terrified her, quite frankly. But she couldn't stay away, couldn't stop the continual urge to have contact with him, just to hear him say her name. He made her feel things, when she had sworn not to feel anything, and although she fought to stay away from him, she found she couldn't. She wasn't strong enough.

She thought she might become strong enough though, when Ana Bakshi came onto the scene. Adam seemed fascinated, hooked by her. Ros didn't like her almost from the first time she was told about her, she would never ever have admitted to being jealous to anyone, but looking back she could see now that she had been, because she knew how Adam felt. She couldn't stay away from him, and he couldn't stay away from Ana.

When she found out Ana was a traitor, a double agent, her first emotion was ridiculous happiness because it meant that Adam would finally see through her. Her second was blind panic when she realised where he was right now. Panic was not something she had ever been accustomed to. The ability to think things through and make calm and rational decisions had been one she was proud of, but that flew out of the window when she furiously attacked Ana Bakshi, desperate to know where Adam was, desperate to get to him in time, her instinct telling her infallibly that something was wrong.

When she found him, drowned in a bath in the hotel room, it was the most scared she had ever been. She had dragged him from the water, blind fear lending her strength and given him mouth to mouth, screaming his name almost hysterically. The panic receded almost instantaneously when, coughing up water, he started to breathe again, and it was replaced by relief, because if Adam was going to die, it wasn't going to be without dignity in some unknown hotel room because of some traitorous woman, and it sure as hell wasn't going to be from drowning.

The next day he couldn't look her in the eye, and despite herself, she felt a stab of satisfaction that she had won this section of whatever game they were playing, that once again she was the strong one. He apologised for putting her in that situation and said that if he had said 'thank you' then he'd meant it. He hadn't, but she didn't bother to call him on it.

And soon after, when she saw a chance to dispatch Ana for good, she took it, telling herself it was for the good of the operation and because it would help them deal with her husband. She believed that too, at least until he called her on it. It was the only the second time he'd been so confrontational towards her and she felt a strange surge of energy when she could fight him, matching him blow for blow, the perfect sparring partner. And it was the first time she realised that he was deceiving himself too, they both were and it was obvious. He was moving closer, until he was right in front of her, telling her it was wrong, that it wasn't safe, that he knew her too well, and when did that even happen? That wasn't supposed to have happened and it scared her. But something in his eyes stopped her from running, stopped her from backing away or making some sarcastic comment. And when he realised she wasn't going to run, he let out a breath of relief, seeming to relax, and his mouth curved into a smile, before he leant forwards to capture her lips in a kiss. She didn't pull away.