Friendship had always been a complicated term for Bolt.

As she watched her new found companions rush down the hill towards this folly, she couldn't help a dreadful sense of déjà vu from washing over her.

It was a terrible fact to admit to, but true nonetheless; everyone who had ever joined her in this seemingly cursed quest to avenge her people was now dead.

Bolt was older than her outward appearance belied. She didn't quite match up to the Time Lord, but she had more than a few years on the human. Her exact age was 150, still young for her people (her ancestral memory reminded her that 1,000 had been considered a good age for a Time Chaser), but for a human, that was more than a lifetime. Testament to that were the humans who she had met and seen through to their personal endings. It was their faces that plagued her mind now as she reminded herself what she had promised after the last one:

This will be the last goodbye.

The curse of her race's perfect memory was that she could remember every previous farewell so clearly, and they haunted her like insistent ghosts, and she couldn't help but think of them on the descent to the ship.

1347 – Kent, England

The first time Bolt had time travelled of her own free will after the first time her people sent her away, she had been only been 20 years old; she'd landed in a medieval farm in Kent, mercifully in the middle of the night, and deep in the midst of a wheat field.

It had taken her ages to simply find her way out of the field and onto the main estate; it was clearly the land of a noble – strip farming was common in these times. Everything had seemed so disorganised and primitive. Bolt had never been on Earth before – and she was only here to investigate one thing; the first recorded use of the exact strand of the death energy that had killed her people. Trouble was, she was alone, on an alien planet, wearing anachronistic clothes, and with technology that might get her lynched in fear. She had made sure straight away that she was presenting as human before even daring to poke her head out of the field.

She might have given up straight away, if she hadn't bumped into Isabella wandering around the fields late at night. Her clothes might have aged her, with her long skirts and her hair wrapped up in a plain hood, but her eyes had sparkled with the mischief of youth – a young adult, Bolt guessed, probably about 18.

"I knew I heard something" she declared, "I met a man here once who appeared just like you – travelled around in a big box though – been waiting to see if he'd come back ever since"

That had confirmed the language and dialect translator Bolt had had microchipped at that mobile tech station a few months ago was working. It had also confirmed why the woman hadn't gone running at the first opportunity.

That is how Bolt had made her first "alien friend" – Isabella, a farmer's daughter. If the human hadn't have taken her in, and given her some clothes to wear, she suspected her adventure might have come to a premature end.

They had spent the next year together, Bolt assumed a new name; Agnes, and in between working for Isabella's father's farm, sought out where the signal she had traced was coming from – searching under cover of darkness usually, with Isabella tagging on by her side. Trouble was, the signal kept moving, as if it didn't want to be found. Bolt had known it was here, but could not figure out what advantage there was in whoever was cultivating it bringing it to such an early period of modern human civilisation.

But despite the delay and uncertainty surrounding the arrangement, and Bolt's undying urgency to find the information she needed and move on, she found it unexpectedly pleasant to have what became a "friend". Isabella was vivacious and intelligent, and objectively good company to investigate with. Without intentionally meaning to, Bolt started to wonder if it wouldn't hurt to take a little longer to find the signal than she had originally intended.

The Panthereon people who had raised her had been stoic, formal, and regimented in their society – and Bolt had grown up to prioritise rules and duty over emotion. She had also been an outsider, a refugee in their close knit society, and whilst she had been accepted and cared for, she had never found affection or friendship with any individual; simply put, it just was not their way. Their sign of welcoming her into their society had been to bite her and, if anything, bestow yet another curse on her life (no matter how willing she had been at the time, it had turned out it mainly just made her life more complicated).

Admittedly, her childhood before the disaster of war had been very different. Her native land was one of close, lifelong, unbreakable bonds that formed for life – to the point that breaking them meant death for both parties. Their very biology dictated that they did not reach full personhood until they reached adult age and completed the bonding process with another Time Chaser.

It wasn't that it was illegal to bond with other species, just unsatisfying and impossible physiologically to attain the same result. There had been one recorded attempt of a Time Chaser trying tried to live life with another species, but they had come back broken and drained after many years, and fallen incurably ill before fading away.

She had known, from a young age, what her purpose was, that she was loved by her parents, revered by her society, and had been destined to a bondmate so strongly, it had been written in prophecy. It had all been so certain, predestined, right…and then fear and meddling had torn up the rulebook, and her life with it.

Bolt had therefore grown up with two extremes – the streamlined order of her foster society, and the carefree adoration of her murdered people. Her nature craved the company of others, but her experience taught her that it always came with a caveat; the pain of losing those you love. So it was with trepidation that she started a new friendship with Isabella, and with the knowledge that she would have to guard against any ill-advised attempts to push it any further than that – both due to the constraints of the time, and because she could never be truly happy with a human as a bondmate, no matter how much she cared for them.

It had all come to a sudden end however far before Bolt could consider what her future in this time would lead to.

They had been getting closer and closer to the signal, to the point where they had tracked it to one specific field. Isabella couldn't see it, but Bolt could; there was a makeshift hut that had been erected with a blue light emanating from it. It had been DNA blocked against humans, same as the ship that Bolt was tracking down in her present time with the Doctor – and neither Isabella, not any of her other community, would ever have seen it, or even had the inclination to get close to it. Just getting close to the hut made Isabella feel uneasy (despite the fact to her, all she could see was a patch of grass), and so Bolt had decided it would be safer for her to come back in the day time on her own, as she didn't know if whatever was stopping Isabella from seeing the hut might also cause her harm if she got too close. Isabella had protested, not wanting to let her friend go alone, but they had left agreeing that Bolt would not do anything drastic without consulting her first.

Bolt went to sleep that night however unable to shake the feeling that they had somehow been noticed.

"If I have brought anything upon you…" she murmured under her breath as she drifted off, "I will never forgive myself for the selfishness of bringing this to your door"

The next day, when Bolt snuck back to the field instead of working, the hut had gone. Worse still, the signal had completely disappeared.

They'd fled.

But why?

Bolt could only think of one answer; whatever they had done, they'd completed, and that meant they'd moved on, and it was probably too late to prevent whatever ill they had produced.

Bolt felt the cold tendrils of panic set in before she had raced back to the community to find chaos.

"It's the black death!"

Bolt held back, and watched from afar, as the townspeople she had lived with for a year had rushed around, proclaiming the presence of swelling and lumps on a number of citizens had appeared. Rumours had been brought in of the dreadful plague ravishing overseas – but nobody had truly been ready for it. Talk began of boarding up homes, burning fires, purifying the air…Bolt could barely keep up, but she was careful to stay hidden and stay far away, she suspected the illness was confined to humans, but couldn't help the nagging feeling that this was a little too convenient that the plague had hit on the same day that the mysterious signal had disappeared.

Had this been the perfect cover for whatever had been planned?

She was too blindsided to think of the answer in the moment. The only person she had wanted to find was Isabella, and once she had got a good idea of what was going on in the town, she ran back to the farm to find Isabella's father in hysterics in the fields.

"My daughter…my only daughter!"

The moment that Bolt had truly understood how much she cared for Isabella had been the moment she had seen Isabella's father in tears, and had known that her friend was going to die.

Bolt had to be held back from going to Isabella's side – it was madness, she knew, and the townsfolk were not about to permit another young woman to become freely infected, but Bolt was unrealistically certain this had something to do with the signal she was investigating. She couldn't be sure how, but she couldn't let her companion pass away uncounted for and alone – she had to care for her, tell her what had happened – try to help…

But in the end, there was nothing you could do against the Black Death.

Bolt spent a grim two days hiding away from the main part of the town, living off what scraps she could manage and in a state of permanent distress, before the news fed back to her that Isabella has succumbed to the plague.

Against her better judgement, she returned back to the civilisation one more time, and from afar saw her friend tossed into a mass grave made for the expected large amount of victims that would inevitably follow. Already, the town that had sheltered her for the past year was being ceremoniously stripped of life – fires burned in the streets and more and more homes were boarded up. It was time to leave.

She knew now that this plague was part of human history, but even until this very day she could never shake the uneasiness that the two events – the signal disappearing and the Black Death arriving, had been linked. She had also never lost the image of Isabella's limp body sliding away, or the emptiness in the pit of her stomach that had only been filled with a weighty sorrow, that she still carried with her to this day.

Bolt wasn't sure if it was her imagination, but she could have also sworn that Isabella's body had a faint bluish tinge to it as it had fallen into the grave. But as she travelled from this cursed time using the Time Energy she had naturally built up over the last year to escape to wherever she could manage, she told herself that it was just her grief imagining things.