The great cat crouched in your front hall, eyes gleaming in the darkness, tail twitching slowly as it watched you. Its body was immense and corded with muscle, its fur striped black and orange. You'd seen tigers at the zoo before, of course, but never this close, and certainly never without a barrier between you. Somehow you'd never realized just how big they were, or how magnificent. You'd heard it said that the tiger, not the lion, truly deserved the title "king of beasts", and right at this moment, you would agree with them. Unfortunately, for the moment that wasn't very comforting.
You raised your hands slowly and tried to back away as the tiger watched you with an unblinking stare. Was that intelligence you saw in its eyes as it regarded you? Had it once been human? Suddenly all those thoughts were driven from your mind as the tiger coiled its limbs and sprang. Before you could react it was on top of you, knocking you to the ground, and then - it was gone, bounding over you and back out through the front door. Groaning you sat back up, wondering just what had happened to you - and then you saw the cut on your hand. The tiger had scratched you, and you'd been infected.
You stumbled to your feet and tried to flee back upstairs when sudden pain struck your midriff. You doubled over in pain as spasms wracked your body, and then, looking down at your hands, you saw the orange and black fur sprouting. It had started. Soon your entire body was covered in fur, and then you could feel the other changes begin. Your muscles expanded under your skin, becoming tightly corded along your frame, and your bones began to rearrange themselves, shifting from a bipideal to quadrepedal configuration. You burst out of your clothes as you grew and now crouched naked on all fours on your floor; a spike of agony suddenly shot through your tailbone and a long, sinuous tail extended behind you and began to thrash slowly. You opened your mouth to groan in pain, but all that came out was a ghastly feline yowling as your face expanded into a muzzle and your teeth grew into fangs, the rest of your features reshaping into a tiger's. As your senses sharpen you can see in the night as clearly as in day, you can smell the musk of the tiger that turned you in the air, and you can hear sounds from across the neighborhood.
You can feel your hands and feet reshape into padded paws and your nails become claws. The transformation is done - or is it? The tiger that attacked you was male, you suddenly realize, though you don't know how you know. That means... between your rear legs your penis and balls suddenly withdrew into your body, and you could feel your internal organs shifting around. Then, it was done. You were a fully-grown tigress. Where once had been a human now stood one of the most dangerous predators on the planet, and you could feel your new body's power as tiger instincts flooded your brain. That's when you realized...