As Doc strolled into the familiar, wooden building of the Hill Valley Post Office that morning, his high expectations and hopes for the day were already beginning to falter. His casual whistling had already droned to a halt as his early morning, high energy began seep out from him, the reality of what he was doing truly only then beginning to dawn on him. In his hand, he held a small, red leather wallet he purchased from the store a few days earlier, tied and sealed tight, a strongly detailed note held tightly in his other hand. Inside was a letter, a single letter three pages long with an attached map and instructions, addressed to his old friend, Marty Mcfly.

Honestly, it had taken too long for him to write the letter – four months, if he remembered correctly, from when he first sparked the idea, not that time was an issue for him here – but he could never seam to get it right. He would have never believed it to be so hard to write one final letter to Marty, summing up all the time they had spent together, everything Marty's friendship meant to him, how much he would miss him, into only a few, short paragraphs. It seamed impossible when he actually came to write it. But he had tried, he had poured his heart and soul into it, and it had to perfect; after all, it was the last Marty was ever going to hear of him.

Doc couldn't believe it had eight months to this day. Eight months since he was catapulted back in time against his will. Eight months since he last saw his friend.

How long it would be until he stopped missing Marty, until the ache in his chest stopped appearing whenever he thought of him Doc could not say.

"Good morning, Emmett. What can I do for you today?" The owner of the post office – not a man he associated with much; he never needed anything posted here in the past – was smiling as usual, his too cheery attitude for once making Doc frown in annoyance.

"Morning Arthur. I need to ask you a favour." Doc was quick to jump to his subject, not in the mood for small talk on such a grey morning. He brought out the leather case and placed it on the counter top.

"Well, as long as it involves mailing letters, I'd be happy to oblige," the man laughed in reply. Doc didn't laugh with him. He didn't even smile. Joking was the last thing he felt like doing.

"Yes... and no," Doc answered cryptically, sliding forward the case so Arthur could take a better look. The man was slow to catch the hint, his smile refusing to fade, but slowly beginning to notice the seriousness in Doc's tone. He picked up the letter and examined it closely, before giving Doc a confused look.

"If you want me to mail this Emmett, I'm going to need an address."

Doc shook his head. "I don't want you to mail it. I need it to be delivered. You see-"

"I'm sorry, that's where you got me. We don't do delivery's here. You know that."

The man tried to hand back the letter, but Doc refused to take it. As they stood frozen over the countertop, letter in between, the cheery owner of the post office's smile faltered for the first time.

"That's why I need this favour Arthur. I need you to deliver this one thing for me. It doesn't even have to be you personally, I just need someone to do it, please."

"Now Emmett-"

"I can pay you if you want. I'll give you the extra money to deliver it for me." Doc was already reaching in his back pocket and drawing out some money. He had brought along an extra twenty dollars just in case the man needed a little persuading, although he had hoped he would be kind enough to simply do this favour for him. Pulling out a five dollar bill, Doc handed it to the man. He couldn't help but smile at the surprised look on his face.

"That's mighty generous Emmett. I'm not sure I could take that from you."

"Please. Take it. All I need in return is for you to deliver that letter to precisely where I say."

There was a moment of silence as the man considered Doc's offer, wavering slightly between greed and inconvenience. In the end it was inevitable which won over.

"It's done." He took the note and stuffed into his coat pocket a little too eagerly before putting down the letter and grabbing a pen and paper to write down Doc's instructions. "Where will I be delivering this letter to?"

"No need to write it down. I already have it here. It's rather long and detailed and I didn't want you to miss anything so I took the liberty of writing it for you," Doc explained, taking the note and placing it on the counter beside the case. "Now listen closely. I need this letter to be delivered on the date of November 12th 1955..."

The confused shock on the man's face did not leave his expression all throughout Doc's explanation. He was utterly lost, looking almost dumbfounded at Doc's words, as though none of what he was saying was sinking in, only washing over him in incomprehension, although the scientist wasn't entirely surprised. It would an almost miracle if he understood what he was saying; some of the vocabulary he was using would not become common place until well into the 20th century. But it was all entirely necessary.

Doc was suddenly extremely glad he had thought to write all of this down to add with the letter. At least now he could be more certain that the details would be noted and understood if anything. But he couldn't help but feel nervous about leaving such an important and dangerous piece of writing – it would catastrophic if anyone were to get their hands on it and dig out the time machine – in the hands of a simple post office clerk. He had no choice but to place all of his trust in the postal service with no way of knowing whether it worked. He would just have to hope Marty would find his way back to 1985 without any inconveniences.

As Doc's explanation drew to a close, and his time to leave and head back to his life in 1885 drew ever closer, Doc couldn't help but feel that same longing ache he always felt at missing Marty sprout in his chest again. He was almost reluctant to hand over the leather case in finality to the man, almost reluctant to admit that it really was best for Marty to go straight back to the future after he fixed the time machine, not to come visit. It suddenly dawned on Doc, with a stab of lonely pain, as if he had not known it was coming for the last eight months, that this really was the last of his friend he was ever going to have, knowing that he would read this letter and travel back safe and sound to the future. Marty was gone. He would read the letter, fix the time machine, and return home safely.

And they would part ways forever. Nothing more than a distant memory in the past now – or was it the future.

As Doc walked from the post office, he couldn't stop the single tear from trickling down his cheek. He just hoped the letter said everything he needed to say.

So for seventy years the letter sat in waiting, rotting, almost like a spirit at the back of the Hill Valley post office. Even as the single, wooden shack grew into the complicated, town postal service that the future held for it, everybody always in a rush to collect, sort, and deliver the mail, the infamous leather case always remained the same. People came and went, owners grew old and passed on their legacy, those that had been there all their lives and knew everything and those that were young, fresh, naive, but the letter always sat at the back, untouched, unchanged.

It grew famous in the eyes of the post office, a joke commonly passed around to the mystery of its owner, who it was to be delivered to, why such intricate instructions had been given, who this 'Marty Mcfly' person even was. ("There's a Mcfly family in town. Maybe he's related to them.") Letters that arrived with no address were often compared to it, said to be as much as a mystery, as tauntingly inexplicable as the thing that hid away on the back shelves.

Ghost stories, made up by the old men who had worked there for too many years to tell the new ones on the job, were spread, of the story behind the letter, how it came to be, how it was delivered by a man, a ghost, who had one last wish, to deliver this letter to his grandson as an adult, the wishes of the dead to pass on their final message. Or a witch, one who could predict the future, who had cursed the letter, causing anyone to open it to fall under a terrible curse.

Nobody ever believed it of course, but there were still those who refused to touch it, those who refused to go near it through superstitious nonsense, claiming the letter simply didn't feel right, something creepy about it, something out of place.

But the question always hung heavy in their minds. Would there really be anyone there when the time came to deliver it? Did this Marty Mcfly really exist?

As the time grew closer, the years ticking by and the rumours passing on, the people of the post office became more superstitious than ever. Suddenly, everything they had long denied as poppycock as to the story behind the letter was surfacing in their need to know the truth. Some were unsure, not wanting a curse hanging over their heads for the rest of their days, some were desperate for answers, anticipating greatly the inevitable day when the time finally arrived.

The early months of 1955 were gone in a flash, dragging, uneventful, and soon the days were being counted down, days until November, days until it was here. They were drawing ever closer and closer to their anticipated answer. Whispers became talk. Rumours became beliefs. Bets were placed.

Arguments quickly sprouted as to who would be the one to deliver the letter when the time came, the idea a curse for some, a privilege for others, but the owner quickly put the sprouting sparks to bed by choosing a man indifferent about the whole matter, who had worked reliably for years with the post office and did not feel the letter was anything more than that, a letter. Whether his interest as to who this Marty Mcfly person was had been sparked by the letter's indefinite time waiting on their back shelves did not matter. He would get the job done. That was all it was, right? A job.

But as he drove out of Hill Valley and down the country road to the allocated spot, slowly, constantly checking his watch to be certain he arrived exactly on time, his apprehension began to rise, and suddenly he was just as anxious as many others to know the truth behind the letter, not that he would ever show it.

The lightning didn't help either, the sudden flashes and thundering sounds only increasing the tension hanging in the air. There was one flash he remembered, just as he was drawing close to the spot, close to the time, one brighter than usual, too bright for lightning, too white, too blinding, the noise not natural for thunder, but it was over in an instant, too soon to even think about. And then the rain came hammering down all at once, just as thought he saw something in the distance, obscuring his view, the rhythmic drumming of the pellets hitting his car roof too disconnected, too jittery for his liking.

His headlights quickly caught a young man standing dead in the middle of the road, the rain pelting down on him without a single care, and he turned as he heard the car coming up the road. A young man, brown hair, wearing a leather jacket and jeans, just like in the description. He knew immediately that this had to be Marty Mcfly.

He stopped, gathering up his umbrella and the mysterious leather case, and stepping out of the car into the pelting rain.

"Marty?!"

As soon the man stepped through the office door he was bombarded with questions; how did it go, was he there, what did the letter say, was it important, who was Marty Mcfly anyway? The man only shrugged in reply.

"Yeah, he was there, just like it said."

He didn't care that the answer was not sufficient to quench the nosy curiosity of most of the people in the post office, they would simply have to live in the dark. He couldn't help but feel the letter was for the man named 'Marty' and for him alone, no one else. He had seamed so happy when he opened it, exclaiming it was from 'The Doc' – whoever that was, presumably an old friend – that he was alive, that he had felt not even himself should have been there to witness its opening. It was too personal for the likes of a stranger like him.

To get away from the angry faces and loud yells, he hustled outside for a quick smoke, needing to relax after the eventful day. He couldn't help but think of the man as he had dashed down the road back into town with everything he had as though it was the most important thing in the world, watching his brief, shadowy figure disappear into the misty rain. Now that he thought about it, the dream-like, hazy memory of it all made him question whether Marty really had been a ghost, after all, if 'The Doc' friend of his had delivered it over seventy years ago, he had to be dead by now, and Marty had clearly shouted how he had been alive.

A thundering noise suddenly brought him out of his thoughts and back into the cold, stormy night of reality. It wasn't thunder, no, it was too artificial for thunder, and the lightning the came with was too bright, too blindingly white to be real. And it didn't come from the sky, it came from the ground, simply around the corner and down the street, distant, most certainly not lightning. It was the second time he had seen it that night.

And he couldn't help but smile in realisation, knowing without a doubt that that unreal lightning and thunder were deeply linked with the leather case that had sat on their back shelves for much too long, had everything to do with the letter, and Marty, and 'The Doc'.