"Rachel, dinner will be ready in about ten minutes!" my mum called up the stairs.

I groaned from my bed, rolled over and opened my bedroom door a crack. "I feel a bit funny, I think I'll skip dinner," I called back. Both my parents had still been at work when I got back from the trip, so I'd grabbed a can of Coke and a pack of crisps; since they both worked until about six, dinner was generally a late affair in our house. Surely you couldn't get food poisoning from a packet of crisps? Besides, I didn't exactly feel sick. More… off. I couldn't think of any way to describe it. I felt uncomfortable- my palms itched horribly, the cut on my arm throbbed and my vision kept slipping in and out of focus. Had I had an allergic reaction to something? Or what if the cut from Kara's claws had got infected? Should I tell my parents? Would I have to go to hospital?

"Honey?" My mum opened my bedroom door. "Oh Rachel! Are you feeling ill? Nauseous? Headache? Do you want some paracetamol?"

"No," I mumbled. "My hands are itchy. I cut myself at the zoo- I fell over and hurt myself while I was looking for my notepad in the tiger enclosure. I dropped it." I managed to piece together the half-lie in my foggy state."

My mum reached out and took my hand, turning it over. The palm was an angry red where I'd been digging my nails in in an effort to stop myself scratching the skin to pieces. "Where's the cut?"

"On my arm."

She pulls up the sleeve to reveal the cut. "Oh, it's only a little one, and it doesn't look infected or anything. You might have had an allergic reaction to something, sweetie, or it could be hay fever. Try and get some sleep, honey. You might feel better in the morning."

I nod and turn onto my back, giving up the battle to keep my eyes open. I feel my mum put her hand on my forehead before quietly leaving my room. After a few seconds, I hear her dialling a number on the home phone in my parents' bedroom and her telling somebody I won't be in school tomorrow before saying goodbye and putting the phone down. It can't be late, then, if she's managed to get hold of the secretary. She usually stays until about five, or later if there's something going on after school. With that thought, I lose consciousness and the blackness of sleep claims me.

I wake in the morning and turn over to look at the time. My digital clock blinks at me from the bookshelf on the opposite wall. 9:38. So even though I do feel better, it's too late to bother going to school now. Even though it is possible for me to get there, my only lesson of the day would be almost over by the time I could make it to the classroom. I turn back over and…

Wait a minute.

I turn back and stare at my clock. The numbers wink at me as clearly as daylight. I get up and rush into the bathroom and stare into the mirror- but no, I can't see the rims of my contact lenses. I didn't accidentally leave them in overnight, so how can I possibly have read my clock? I'm short-sighted; usually the numbers look all blurry and I have to concentrate on them for up to a minute before I can work out what they are. So why are they suddenly clear?

I look back into the mirror and gasp. How could I not have noticed before? My eyes… they've changed. Their usual hazel colour is gone and in its place is a golden yellow. Tiger eyes.

No!

I run back into my bedroom, pull my animal encyclopaedia down from the shelf, scan the index and flick to the section on tigers. On the first page, a large colour photograph of a tiger's face stares back at me. Its eyes bore into mine, the yellow in its eyes more bronze than golden. But the point is still the same. I turn through the other pages, my brain barely comprehending what this means, and find a picture of a tigress with paler eyes. Like mine.

I put the book back and a sudden tingling begins in my hands. Before my newly-enhanced eyes, the skin on my fingers and palms begins to change. It becomes darker in colour, almost black, and becomes tougher and harder.

I've just grown pads on my hands.

Whoah. My head spins and I've got to sit down for a minute. I drop onto my bed and cradle my head in my hands. Just what is happening to me? Am I turning into a tiger? Has this kind of thing ever happened to anyone before? I take my hands away and breathe evenly to stop myself from freaking out, allowing my scientific side to kick in. Calm down Rachel. Assess the facts. What's happened to you?

You've got yellow eyes and improved vision. Tigers have round, black pupils surrounded by yellow irises, and their vision is undoubtedly more powerful than a normal human, let alone a short-sighted one.

You've got pads on your hands and feet. All cat species have pads on their paws to support their feet and cushion their load-bearing limbs.

I bite the inside of my mouth, like I often do when I'm thinking, and wince. The sour tang of blood flows onto my tongue and I move into the bathroom to inspect the damage in the mirror. I grab some toilet paper off the roll and dab the inside of my gums with it. I must have bitten my mouth really hard…

Oh. Another freaky thing to add to the list. My canines have grown sharper and longer- a tiger's canines can be as long as 74.5mm, and they've even been known to be up to 90mm in their total length. Thankfully mine aren't that long, but I have to open my mouth to almost yawning size before my top and bottom canines don't touch. Oh God, I hope nobody notices. They'll be calling me a vampire next, and there is no way I'm going to be associated with bloodsucking monsters for the rest of my life. Or- sorry, Edward, I do think you're hot and what your family does is cool- the Cullens. Crap- I've got yellow eyes too now.

"I'm not a bloody vampire!" I mutter under my breath. "I've just been scratched by a genetically modified tiger which has then licked the scratches to heal me and passed some of its DNA into me. Because that's much less weird."

I go into my bedroom, strip and throw my pyjamas onto my bed before pulling on a t-shirt and some jeans, before going downstairs and pouring myself a bowl of cereal, which I sit munching at the table. So what are you going to do? I ask myself. For starters, there is no way I'm telling Mum or Dad about this. There's no way I'm telling anyone. They'd lock me up in the zoo with the tigers and carry experiments out on me. Although… should I tell Sara? The staff working with the tigers wanted to know if the use of their healing saliva would have any side effects. Clearly they do, so should I tell them? No, they can find out on their own. I need to figure out what's happened to me. Give it a few weeks and I'll think about it again then.

Suddenly, I remember a fact from my research and a smile spreads across my face. Tigers can run between thirty-five and forty miles an hour. If I've gained some of the physical traits of a tiger, who's to say I haven't got some of their other traits too?

I dash out of my bedroom, run downstairs and out of the front door, down the steps and onto the pavement. I live on York Street, which is around the corner from a very expensive street called Montagu Mansions, full of expensive looking flats. Our house is just around the corner, a cream front with a black front door nestled among the red brick of the Montagu flats and cream and grey of the rest of the street. Our house looks small and squashed in among the rest of the flats, but I think it's the best one- at least we've got two floors, which a lot of people don't have. Our road also connects to Baker Street, where Sherlock Holmes lives, which, being a huge Benedict Cumberbatch fan, is pretty awesome. We're also only a few streets away from Regent's Park, which hopefully shouldn't have too many dog walkers at half past ten on a weekday. Most of London's busy residents will be at work by now, so that's where I go, forcing myself to walk and resisting the urge to start running.

I pick the quietest spot and hide myself in the trees, just in case. I take a deep breath, rock on my toes, and start running.

To my surprise, I leap like a stone rocketing out of a slingshot- or should I say, a tiger leaping out of the bushes. I pick up speed but I can see the details of everything moving past me with startling clarity. Do I have normal human sight now, or is it more advanced? Surely everyday people who don't need glasses can't see like this? My instincts take over and I see a large, sturdy tree. Before I even know I've decided to do it, I've changed direction and leapt onto the tree. To my surprise, I cling there and realise that claws have extended from my hands. I shudder and retract them without thinking, sending myself tumbling to the ground; luckily only a few feet below me. I sit up, puzzled. Tigers aren't notorious for being good at climbing. They're better at running fast and swimming. Then I remember the DNA from the black leopards Sara talked about. Their climbing ability is unequalled among the wild cats, even when carrying a carcass, as is their stealth. Although clearly I have the talents of a wild cat, but not the instincts to go with them, as I'm pretty sure a black leopard wouldn't have released his hold like that without thinking about it. I'll have to practice.

I stand up and brush leaves and dirt off my clothes. I grin and burst into a run, jinking sideways through the trees and leaping fallen trunks and bushes with ease. I slow to a human jog as I get out onto the pavement and glance upwards at the buildings. I wonder… horizontal leaps by tigers have been recorded up to ten metres, although they're usually less than this. Some of the buildings in London are very close together, I'm sure I could make it if I tried…

My watch beeps and I glance at it. It's midday! I'm sure I remember Mum mentioning something about coming home to check on me in her lunch break before she left this morning! I start sprinting for home, resisting the urge to run faster and faster. Is this what tigers feel like when they're in wide open spaces? I restrict my running to human speeds and make it home in about five minutes, leaping the steps and unlocking the door. I close it behind me and listen for movement. Nobody's home, so I go into the kitchen and make myself a sandwich. All the running has made me hungry and my stomach growls as I grab the butter and ham out of the fridge.

I've just finished my sandwiches when I hear a key turn in the front door. I open the pack of crisps and try to act casual as my mum walks up the stairs and knocks on my door.

"Come in!" I call.

"How are you feeling?" she asks anxiously as she opens the door and sits down on my bed.

"Much better," I say, hoping she doesn't notice the colour of my eyes and trying not to smile too much so she doesn't see my teeth.

"Hmm." She puts her hand on my forehead. "Well you certainly feel cooler than you did yesterday. Have you had any fresh air?"

"I went out for a walk to the park earlier," I half-lie. After all, I did go to the park; I just didn't do much walking.

"Good," she smiles. "Well, I'd better get back to work. Remember not to answer the door to anyone unless it's one of your friends, and try not to get into trouble."

I roll my eyes but laugh. "Yes Mum, I won't Mum. See you later."

"See you later."

I wait for the sound of my Mum's car driving away before leaping up, checking I have my keys and phone and running out the front door. Time to find the closest buildings in London and practice some jumping.

"Wahoo!" I scream as I leap into the air, my arms flailing and my hair blowing out behind me. I plummet towards the roof of the next building and land in a crouch. It's amazing how I can leap so far and so high, yet land with the gracefulness of a tiger, barely making a sound. I balance on the balls of my feet before running forward again. As I near the next building I realise it's way too high for me to leap to, but my body adjusts itself and I take off, flinging myself at the side of the stone expanse. My claws slide out of my fingers and dig into the grooves in the brick, securing me to the side of the building. My shoes don't afford me as much grip and I resist the urge to kick them off. I'm two hundred feet above street level, and below me is a road busy with cars and buses. I'd probably never find them again, so I leave them on.

A delicious scent suddenly reaches my nose and my mouth begins to water. I glance down and see a burger stand further along the street underneath me, and a man stands nearby eating a bacon roll. The temptation to swing down there and tear it out of his hands almost overwhelms me and my body shifts to move…

Whoah. I need to stop this. I tear my eyes away from the burger stand and breathe deeply, forcing my thoughts to focus on something else. If I appeared out of nowhere and grabbed the roll off him before running away at superhuman speeds, I'd attract attention and people would see me. There might even be a chance someone would recognise me, or somebody could report me to a news station, and then my cover would be blown. I need to keep my abilities a secret if I want to live what appears to be a normal human life. Besides, if I end up locked up in a lab, I'll never be able to go to university and help save the lives of abandoned animals like those dogs. I sigh and clamber up the building to the roof, avoiding the windows in case anybody happens to be standing on the other side.

I stand and look around until I locate the streets near my home before taking off, using the rooftops to get home without being seen. I climb down the side of the Montagu flats and leap the rest of the way when I get close enough before disappearing inside my house and up to my room and collapsing on my bed. Exhaustion from all the running and jumping sets in and before I know it I've fallen asleep.