Disclaimer: I do not own X-Men: First Class. I do own Emily Hope, however. The title means 'Time Flies' in Latin.
Emily Hope (codename Tempus) isn't a genius, an athlete, or a trust fund baby. She is average, with a normal family, normal problems, and she would have gone on to lead a singularly normal life if not for one fact. She is a mutant, a person with a mutated gene, commonly known as the x-gene. It was a trait passed down paternally, though she was the first in her family that the gene had manifested in to gain powers.
Her powers were something interesting. She could travel through time; a more accurate description would be that she had the unique ability to manipulate time in such a way that she could relive events in the past and alter those events should she see fit to do so. It only went the one way, however. She couldn't travel to the future, so if she went back in time for, say, a day, she had to relive that day over until the timeline caught up to when she had disappeared. She could also change location, if she concentrated hard enough.
Professor Xavier speculated that the reason she couldn't travel forward in time was that the future was being changed with every decision every person in the world made. It involved a lot of thinking in circles and abstract ideas, and it hurt her head to think about it too much. She was fine with not being able to go into the future, though.
She never thought that she would have any reason to travel back in time for more than a day, but things change and one day changed everything.
It was war, plain and simple. The humans' fear of mutants had finally come to a head, resulting in rioting in the streets and attacking of known mutants. The X-Men had been called to help a group of mutants trapped in a building by a bunch of humans threatening to burn them all. Professor X had come as well, in the hope of talking to the humans and offering the mutants sanctuary. No one was quite sure how Magneto had heard about it, but he was there, along with his brotherhood of mutants.
It was madness. The X-Men were fighting Magneto's mutants, who were fighting the humans, who in turn were fighting all the mutants, including the X-Men, who were trying to protect the humans from Magneto's mutants. Emily was standing by Professor X, who was looking into people's minds and warning the X-Men of upcoming attacks. Emily was a part of the X-Men, though her powers weren't needed unless someone was seriously injured or about to die, then she'd jump back in time and try to prevent it. The unofficial rule to time-travelling was that you could jump back to a point three times, before you were done. Why three, she didn't know, but she had realized that she could circumvent the rule by jumping slightly farther behind or forward than the point she had previously. Thankfully, her power hadn't been needed yet in this battle, but she knew it was only a matter of time.
She winced as she watched Cyclops take a metal rod to the head, courtesy of a human. Jean used her telekinesis to throw the human away from Cyclops before moving to check that he was alright. Emily let out a sigh of relief as she saw Cyclops get back on his feet, if a little unsteadily. Rogue was using the ability to manipulate fire that she had stolen from Pyro to extinguish the small fires the humans had managed to set. Iceman was freezing humans and mutants alike to prevent them from fighting, though he looked as if he was tiring. Storm was blowing the humans away from mutants with strong winds and sending down lightning bolts at Mystique, who was also dodging Wolverine's claws, while Nightcrawler was transporting the mutants out of the building and away from the fight, if they wanted to go. Some wished to stay and fight against the humans. Shadowcat was assisting him by phasing the mutants through the walls of the building and away from the fighting.
Magneto had been attacking humans and the X-Men with everything from the guns the humans had brought to cars parked on the street. Professor X had tried reasoning with him, shouting to be heard above the chaos, but Magneto would not be deterred from his way of thinking. Eventually, the professor had given up and focused on helping the humans and other mutants, but Emily saw him shooting glances at Magneto occasionally. She had asked him if he wanted her to go back in time and find some way of removing Magneto's helmet, though she didn't know how, but he had refused, insisting her powers were better used for helping the others.
The area where she and the professor were standing overlooked the battle going on below. It was a small cliff built jutting out from the side of a larger cliff. Emily glanced up as a small piece of rock fell down the cliff and bounced harmlessly against her shoe. She was nervous about this position, as any number of attacks from the mutants below could bring those rocks down on her and the professor. If that happened, she hoped she was quick enough to transport to the past and prevent it, somehow. She said as much to Professor X.
Of course, Emily should have never voiced her concern to the professor, as saying it just guaranteed that it would come true. She wasn't entirely sure how it had happened, though if asked later, she would have sworn she saw a flash of red hit the cliff. One minute, she was staring at an increasingly horrific battle between mutants and humans, and the next she was looking at a ton of rock and gravel barreling down on her and the professor from above. Instinctually, she started to call on her power to jump into the past, mind scrambling for a proper time. She was just starting to concentrate, her hand on the professor's shoulder to reassure him she was moving to prevent the avalanche of debris, when she felt something smack her on the head, hard. Whether it was a rock or something else entirely, she didn't know, but the impact was enough to break her concentration mid-jump, sending her thoughts awry and causing her to unconsciously tighten her grip on the professor's shoulder.
She was starting to panic now, and that panic was causing her mind to resist the time she had been thinking about. Her thoughts were too many, too quick and she couldn't concentrate. She could vaguely hear the professor's thoughts, not sure if he was knowingly projecting them. He was wishing none of this had started, not just this battle, but the whole war. He was thinking, strangely, about a smaller battle on a beach in…Cuba? And who was that lean gentleman wearing Magneto's helmet? And that younger man with shaggy brown hair and his hand to his head…Professor X?
As Emily's mind focused on the memories from the professor, her powers were reacting to the situation and traveling through time to remove the girl and the man whose shoulder she had in a death grip from their perilous place on the cliff. It was really no surprise later when she thought about it that her powers had latched onto the memories from the professor and transported her to that place on the beach so very long ago. What was a surprise was that they brought the professor along for the ride.