When Sam's deployment information came through a few days later, she was filled with the same mix of excitement and trepidation that she'd felt as a young medic in the RAMC. This time though, things were a little different.

"I'll fly out from Brize on the third of November," she said to Dylan over her little kitchen table. Her eyes scanned her laptop screen. "Four-month deployment, and – oh."

"What is it?" Dylan frowned in concern.

"No – I sort of expected this. It's a short deployment, so there's no leave planned. I'll miss Christmas."

"Oh." He understood her disappointment: it would have been their first Christmas back together as a couple. "It's okay, I will just send a present out to you and we'll have 'Christmas' in March, when you come home," he said practically. "I'm sure forces couples have done worse and weirder than that, before now."

"There'll be no emails," Sam added. "Too risky, the IP address could be hacked too easily and our location determined."
"Can we write, instead?"

"Um, hold on," she said, casting her eyes along the small print. "Yes, thank god. Plain old blueys, so you better start smartening up your handwriting."

"Rude, you know my penmanship is flawless," Dylan said in mock offence.

"Oh yeah," she teased. "When you're not in a rush, otherwise it's dead spiders rolling in ink and across your page!" She was joking, of course, but there was something off in her tone.

Dylan nudged her ankle under the table, with his foot. "Okay?" he checked.

"Yeah, only… I'd forgotten how it feels to see it all laid out in black and white."

He reached over and closed the laptop before taking her hands. "Little bit overwhelming?"

She nodded. "It's a lot."

"You'll be okay. You were always the same, except with longer to mull it over and acclimatise. How long is it now, two weeks?"

"Mm-hm. Thirteen days."

"So, when were you planning on telling me you were going out again?"

Sam closed her notebook with a little more force than intended, keen to keep its contents to herself. She spun around on her stool to face Iain. "I wasn't trying to keep it from you," she said. "It all came about so quickly and I didn't know how to tell you." She held her notebook tightly in her lap; seizing a few spare minutes from this shift, she had used the quiet of the ambulance station to continue making lists and force herself to think about her most important pre-deployment task. "God, was there always so much to sort out before we went?"

Iain cracked a smile. "Course there was. But we had a couple of months to do it, and we were never working in the NHS at the same time!"

On this matter, Sam had been insistent. She wasn't going to be an inconvenience until she absolutely had to – she would have worked right up to her deployment date if no-one had challenged her over it. Fortunately, this hadn't been necessary. A natural break in her shift pattern meant she would finish work as a paramedic exactly three days before deploying.

"You're mad," Iain said affectionately as he headed for the kettle. "But you know what, all hats off to you. I mean it, Sam, there's no way you'd ever get me out there again. But you'll be amazing, I know it."

Sam looked down with a muted smile. "You remember the stuff we had to do before we left home, don't you?" she asked quietly.

Her shift in tone meant he knew exactly what she alluded to. "I do," he replied. "Always too me bloody ages to write those letters. You struggling?"

Sam pressed her lips together and nodded. "I can't write one for you," she said quickly, the words like champagne foam propelled forth past a loose cork. "I've been thinking about it for days and there's nothing you don't already know. I can't write down how important it is that you're still my friend. There aren't words for that."

Iain's expression softened. This was so typically Sam, getting her goodbye out of the way so that she could finish her work without it hanging over her. "You be careful out there, alright?" he said, raising one eyebrow. "Come here." He opened his arms to hug her. A lot of unspoken words passed in that embrace. There'd been a lot of history.

Sam held the plastic-wrapped packages tightly. That afternoon, with eight days to go until her deployment, she had collected her new issue of winter uniform. Although slightly different to the sand-coloured t-shirts of her Afghanistan tours, she still had butterflies in her stomach as she held the weight of this important clothing and all it represented.

In five days, she would work her final paramedic shift and in seven, she and Dylan would make the journey to Oxford, just as they had done as a married couple all those years ago. The prime difference however, would be the standard of the hotel for their final night together. This had been at Dylan's insistence, a claim that he at least was too old for a cheap room with a lumpy bed. She had reminded him that she was hardly heading out to five-star accommodation courtesy of the RAMC, but this had only strengthened his conviction that her last sleep on British soil would be a comfortable one.

She still hadn't written her letter for him, and she was running out of time. While this deployment was somewhat safer than landing in Helmand Province, Sam would not allow herself to become complacent. The information she'd received further to her deployment details, she had not been allowed to share. It looked likely she'd be working very near to the Poland-Ukraine border, supporting refugees immediately after fleeing their home country. The closer to that border, the closer to an active warzone. It was a humanitarian mission but that did not mean it was without risk.

That evening, she was alone in her flat for the first time since her medical. Since then, she and Dylan had been (with wordless agreement) largely inseparable, spending nights together either in her flat or on the boat. It had suited her perfectly, quelling her unexpressed anxiety around going away and allowing her to learn him by heart, making sure she would always be able to call him to mind when they were apart.

But that night found him on a night shift, so she set to thinking about writing the all-important letter. It was her last one: she'd done her other three relatively quickly. One for her parents (whom she had not been in touch with in several months) and one each for Nick and Zoe. While it hadn't been emotionally an easy task to write those, the words had flowed and she had managed to say exactly what she intended. Typically, it was infinitely more difficult where Dylan was concerned. There was so much that she would want him to know, if she wasn't coming home to him when this was all over. She didn't know enough ways to say that she loved him and that she wished they'd had more time.

She was deep in thought, staring into space, when the words seemed to arrive by magic in her mind. She pulled her blanket closer around her, drawing her legs up onto the sofa, and began to write.

As the words poured out onto the paper, so too did about fifteen years of emotion. Sometimes she beamed, calling to mind a particularly warm memory. Sometimes she had to set the notebook aside and cry, as it struck her, the enormity of what she was doing. The letter would only be read in the event of her death, a possibility so horrific that she hardly dared think about it for a moment. And sometimes she couldn't stem the tide of tears at her own unwanted imaginings of how Dylan would cope if she was really gone forever, after these precious few months back together. These kinds of thoughts had barely registered at twenty-two, when she'd invincibly set off for the Middle East, determined that nothing could possibly stop her from coming home. Age had stripped Sam of this naivety, making it vital that things were not left unsaid.

When she was finished, she held the sealed envelope over her heart for a few moments, hoping with everything she had that the letter would never have to see the light of day again.

Emotionally exhausted, she started the nightly routine of switching off lights and checking doors and windows. She retreated to her bedroom and switched on her soft lamp and the radio, her quiet companion in an empty flat.

It was her final run of shifts. Four consecutive days – two short and two long – and she'd be done. To the amazement of the ED, however, it was as though nothing was different. Sam ploughed herself into work and if anything was more focused that before what would be forgiven for becoming an enormous distraction.

At the end of her first long day, she headed for her locker to retrieve Dylan's letter. She would spend the night with him on the boat, and she would hand over this letter with its strict instructions.

"I will miss you, you know?"

Sam turned and closed her locker at the sound of a thick Welsh accent. To her surprise, Jan seemed a little sheepish.

"I know I've been a grumpy bugger and not said anything about it since you came to me with your forms and whatnot. But that's not to do with you, and I shouldn't have been difficult about it."

"You haven't been, it's fine," Sam said quickly. True, Jan had been a little prickly, but Sam had rather expected as much.

"I'm pleased for you, that you're getting the chance to do what you love, even if I'm losing a paramedic for it." She gave a wry smile.

Sam returned half a smile, sliding the envelope into her back pocket and out of view. "I'll be back in four months! End of March and you'll have your team back."

"Not if that man of yours has an ounce of sense about him. Do you really think he'll pass up the chance of an extra doctor in that ED, never mind one with your trauma skills?"

"I… hadn't thought about that," Sam replied honestly.

"Well, give it some thought," Jan said firmly. "You're bloody good at what you do, and you shouldn't be on an ambulance if you want to be back in an ED."

Though her perception of possibility was shifting beneath her feet, Sam projected utmost confidence. "Anyone'd think you're trying to get rid of me!" she joked.

"Oh, give over!" Jan replied with a chuckle. "It'll be like tying a hand behind our backs, but life's too short not to do what you love." Her tone became more serious. "Life's too short," she repeated pensively. "I'm not on tomorrow, Sam. Be careful, alright? I want you back here in one piece, whether you're still here in green or whether you're in a pair of scrubs. Look after yourself."

Her meaningful nod felt like the end of a chapter.

"I don't know why I don't just give you a key," Dylan muttered as he let her inside.

She unzipped her coat and hug it on what had become her hook. "Well it would be a bit pointless now, considering I'm about to be away for four months," she said lightly, reaching for his hand with both of hers.

He flinched. "Christ, woman, don't you ever have warm hands?"

The temperature difference between the dark quayside and the softly lit boat was striking. Sam was grateful for the log burner – such luxury would be scarce, this time next week.

"Well, I will, once I'm changed and under a blanket, with a cup of tea," she mused, thinking longingly of her pyjamas. She felt around in her pockets for her phone and flat keys, and remembered the letter. Her mouth dried a little. Now was not the time to go to pieces.

She followed Dylan over to his little kitchen, the envelope held in a hand that she refused to allow to shake. He was busy filling the kettle, but as he reached to turn it on, she pulled his hand away from the switch.

"Just a minute," she said quietly. "I need to give you this, and I need you to put it somewhere safe."

Dylan frowned in confusion. Not understanding, he slipped his finger under the envelope flap to open it.

Sam reached out quickly. "No – don't open it! I should have written on the envelope, I'm out of practice with this."

"Sam?" His voice was heavy with concern. "This isn't – it's not what I think it is, is it?"

Despite her best effort, she felt her eyes begin to prickle. "You need to put this somewhere safe, and promise me that you won't open it unless I'm not coming home alive."

It was a shock to her system, seeing immediate, deep emotions on his face. He swallowed hard. The letter in one hand, he used the other to pinch the bridge of his nose while he squeezed his eyes shut.

"I had myself convinced that you wouldn't write one this time," he said thickly. "I told myself a humanitarian mission would be safe..." He sniffed.

Sam's heart leapt into her mouth. "There's always a chance, Dylan," she replied softly.

Though she did not cry, she did gasp when he suddenly wrapped his arms around her and held her like he never wanted to let her go.

"What about all the things I'd want you to know, if – if you weren't coming back?" he whispered.

Sam let out a sad laugh. "I don't think a letter the other way would fulfil its purpose," she said weakly.

He responded with what felt like a laugh reverberating through his embrace. But she quickly realised they weren't laughs at all, but silent sobs.

"Oh Dylan, my beautiful grump," Sam murmured. "How long have you been waiting for this?"

That night, they were in a safe embrace in bed, when a thought occurred to Sam. "You never cried at any of the other letters," she observed. "What's different this time?"

Dylan kissed the back of her neck. "Correction – I never cried over the letters to your knowledge. They broke me every time: I just managed to hold it together until you'd gone."