Mike turned when he hear the shout, and saw the stable owner with a group of other villagers, all running toward you. "We REALLY insist you stay, HORSE-BOY!"
Although Mike was no coward, he had a bad feeling in his gut, and spun around to gallop off. Unfortunately, several of the villagers had already let fly with ropes that caught his hind legs. The ropes were seized and jerked by the mob, sending the centaur sprawling heavily on the dirt road.
He tried to get up, but a young man leaped on top of him and swung something at his head...
Mike woke in a large, dark stall. The windows were barred and shuttered, and the walls and door were made of thick, heavy timbers. The bedding was old and dirty, and the air was thick with flies and the stink of urine and manure. He rolled up to all fours, feeling disoriented and awkward, and shook a thick head.
As his eyes adjusted to the dark, he made out a very faint glow from his chest. It was hard to turn his head far enough, but he finally made out a bluish pendant hanging from his neck. It was a figurine of a thick-bodied horse, some sort of draft breed. Then he realized that the skin under the figurine was covered in shaggy black horse hide.
He felt his chest, and then his face with a moan of fear. His formerly human upper body was fully covered in fur, and his face was pushed out and swollen. Although he still had arms, they felt smaller and weaker. He was turning into a horse!
It had to be the pendant! Mike grabbed at the glowing object to yank it off, only to feel a shock in that hand. His whole right arm shrivelled to the size of an infant's, drawing into a shoulder that was melting away.
He screamed and kicked at the heavy walls, but got no response. Panting, Mike twisted around to look at himself. His horse parts were emormous, and beautiful even in the dark. Glossy black hide and brilliant white feathering marked the breed as a Shire, and he could feel that he was still a stallion. In fact, his organ was dropping in repsonse to pressure in his bladder.
Mike tried to stop himself, not wanting to soil the stall like an animal. His body ignored the commands to stop, and he automatically leaned forward as he let loose with a hard stream of piss. Then his tail lifted, and he added to the solid deposits as well. Shaken, Mike realized that he had lost all control of bodily functions. His mind was changing along with his body - and when the transformation was done, he would probably be a stallion in thought as well as form.