What would you do if your grandmother gave you a diary which listed dates and locations of events that were going to happen in the future? Would you go to the locations at the proposed times? And what would you do when you realised your grandparents were there too, only they were clearly younger and undoubtedly didn't know who you were?

The first time I saw my grandmother Amelia as a young woman I was sitting on a park bench in Leadworth and saw her walking past. At first I didn't even recognise her, and I would have completely missed her but her red hair, iridescent in the sunlight caught my eye and I remember thinking it was the exact same shade as my grandmother's hair. As I watched her walk past, so close I felt I could reach out and touch her, I realised that she looked exactly like an old photograph of my grandmothers that used to sit in the hallway of my childhood home. I used to stare at it as a child, transfixed in the way all children are when they see a grown up when they used to be young and free and beautiful.

"Amy" a voice cried "Wait up. Where are you going?"

A young woman about the same age as the redhead ran up behind her and she stopped and waited for her. The force of a thousand shocks rushed through my body, I almost cried out in surprise. How could my grandmother know about this woman walking in the park decades after she'd died, in a different country no less? This woman, a wild beautiful creature looked just like my grandmother in her youth and she had the same name too?

Could the stories I'd been told been true? Of all the reasons in the world that my grandmother knew about this moment that she could have set up an elaborate hoax or have been a physic who could see the future. Could the real reason be because she, my grandmother, was the young beautiful woman who walked past me?

My mind denied it but my instincts screamed it. This woman was, she must be, my grandmother.

I didn't know my grandmother was a time traveller growing up; in fact the secret had been kept from me until after she died. Dad had told me, in hushed tones, of his parent's secret. They, especially my grandmother had known for a long time that I would meet them in the future, my future...their past. She'd told dad that it had just suddenly flashed before her when I was about 10 that she had seen my face before. I was the mysterious girl who had shown up at random locations, watching her and granddad, sometimes taking on the role of background extra, at other times being a core participator of the scene.

She had called me The Extra.

Once she realised who I was going to be, she'd started writing down dates, times and locations in a diary of events that had happened in her life. She'd called the diary The Future Diary of Amelia. It was always sitting in a book shelf in our sitting room and on odd occasions, when a memory came to her I guess, she'd get out the book and write a new event in it.

The diary lay in my lap as I sat on the bench. I had suddenly felt ill and wanted to throw up but stayed as still and inconspicuous as I could, lest I give away my secret.

"Hey Mels" Amelia, my youthful grandmother had replied. "I'm just going to hang out with Rory"

"Rory hey? Well, I'm not surprised considering all that smooching you guys did at the school dance" Mels said, grinning widely.

I feel the need to add as an afterthought that it was some time later that I discovered that this woman was in fact my Aunt River. I don't know all the details yet but she had apparently changed her entire appearance and personality into the Aunt I knew sometime before I was born. There was always something really odd about her, and her husband too apparently, although I'd never met him, the fact that my aunty never seemed to age was the first giveaway. Her husband was just a character I'd heard about and never met until these street encounters, he was never around when I was a child and my grandmother and aunt would sometimes talk about him.

Once I asked why he never visited us and Aunt River turned to me, smiled and said "Spoilers".

Amelia and Mels walked off together, Amelia elbowing her friend affectionately. They talked as they left but I couldn't catch anymore of their conversation. My hands still shaking from the shock of my discovery grabbed at the diary and I opened it to the first entry; today's date and reread it. After the date, and location was the following:

First official date with Rory. A quick walk across the park to Rory's house. I'm feeling nervous and slightly embarrassed but mostly I'm worried he really is gay after all and this whole thing is going to ruin our friendship. Wait around for your answer.

The time had said 6.45pm – 8pm but the walk by had only taken less than five minutes. Perhaps my grandmother had gotten the times confused and wasn't exactly sure when she'd been walking past so had given me a general time. I sat for a little while longer, trying to process all that I had seen. Up until now I'd never really paid any attention to dad's stories, nor the diary which had all seemed a little silly and fairytale. After all, the whole "your grandparents are time travellers" had never really made sense and I'd always taken it for a metaphor for something I never could quite work out.

But no, they were actually time travellers. Actual, actual, from the future and had travelled in time and space all over the universe. Even grandmothers story of another parallel existence where she'd lived for 36 years in a day with only a robot for company started to have an air of probability (although she said even though it was true and had happened she couldn't remember it as that version of her had never existed as she'd been saved right away).

Oh how I wished she was alive right now so I could talk to her about it. I suddenly had a deep yearning for the grandmother I knew, the one who'd baked for me and told me the best stories about aliens and space travel.

A tear slipped down my cheek and I wiped it away, determined to leave while I still had my composure. Just as I was about to stand up Amy came back, this time with Rory, my now youthful grandfather. How young they both looked, younger than even I was right then.

They walked over to the grass, Rory carrying a chequered blanket and picnic basket and looking so nervous I was sure he'd burst into tears then and there. They laid the picnic blanket out and sat down. This was the extra time she'd written in the diary, their first real date, a picnic in the village that they livid in. I took out my phone and discreetly snapped some pictures of them with it. Both were oblivious to my presence and I felt like I was intruding in their special moment until I remembered that I'd been invited and that later on in her old age my grandmother had wanted me to see this.

They stayed chatting and laughing together for about an hour before packing up and walking back in the direction of the town square and I stayed a moment longer before leaving. Before I left I checked the next date in the diary. It took place two days after in London so I hadn't time to stay in Leadworth in the hopes to see them both again. This time my grandmother had drawn a map of the Thames with the ideal spot for me to hide to watch the action, it read:

Battle with a giant sea monster in the River Thames. Hide in the exact spot indicated; close enough to see the action but far enough away to avoid being eaten. I KNOW you'll be fine.