Booking

He fell to the ground clutching his stomach tightly in one arm, grunting in pain between the gasps for air as he coughed up blood.
"Oh my god, I'm so sorry, I had no idea. Sam, Sam say something." Kirk said still holding the warm leather bound book nervously in his hands.
"Aaaaarrrgggghhhh!" Sam cried as he threw his head back; several large bright green scales had erupted out of his eyebrows. Sam raised his other hand over the rapidly lengthening protrusions as its back began to ripple and stretch. Kirk stumbled backwards letting the book drop out of his hands. It landed on the ground lightly and immediately sealed itself up. Sam let out another yell as he doubled over again, the back of his shirt being stretched by unseen bulges. Suddenly there was a ripping sound as Sam's trainers burst. Large ivory claws grew rapidly out of the toes and heals of each foot. As Kirk watched, continuing to slowly back away, Sam's jeans began to push out until they too ripped; revealing a steadily growing green, scaly tail. Sam let out a deep guttural groan as the bulges on his back grew too big for his shirt; ripping it in two. He dug his nails into the floor as his fingers fused together leaving three thick structures in their place, on the end of each grew a long bone like talon. Scales burst through his hands writhing skin as a row of long green spikes erupted along Sam's spine. He roared an unearthly roar as with a loud crack his face pushed forward into a snout. By now Kirk had reached the wall of the room they were in and had started to sob loudly. "Oh god, oh god, oh god. I'm so sorry." He whimpered to himself as he saw his friend's jeans stretch and then finally burst as Sam's mass increased dramatically. His normally slender arms and legs were replaced by huge muscular monoliths of power. The bulges on his back grew tall and slender until finally opening out into a pair of large scaly wings. Sam's well kept teeth rapidly merged into a row of evil looking shredders as hundreds of green scales erupted out of his straining skin to cover what wasn't already. Sam lay on the floor all motion stopped, the transformation evidently having ended.
"Sam? Is that still you?" Kirk asked wiping his tears from his face. The creature turned to look at Kirk sharply and stared at him through cold animal like eyes. It suddenly roared loudly before jumping into the air and with a loud crash flew through the roof and away from sight. Kirk was left alone in the room, not even the book remained as it had mysteriously vanished.