All of this was fine until a spy from another country managed to steal a container of nanites. The spy managed to escape to New York City where he planned to sneak out of the country.
Mark was an FBI agent on the trail of this criminal. Mark didn't know what the spy had stolen. All he knew was the spy had stolen some technology that couldn't be allowed to fall into the wrong hands.
Mark caught up with the spy at a subway station. The spy was staying in crowded places so that the FBI would be reluctant to start a gun fight. Mark followed him for a while but he knew he had to make a move soon before the spy gave him the slip. When they got to a station that was less crowded, Mark pulled his gun and yelled, "Freeze, whoever you are."
The spy chose to run and barely managed to dodge the bullet. It grazed his left shoulder and blood started spewing out. The spy grabbed a woman who was holding hands with two small children. The spy used the woman as a shield as he backed away toward the darker parts of the tunnel. Mark had called for backup but knew they probably hadn't arrived yet. He was in a standoff. He told the kids to sit on a nearby bench and wait but he didn't dare take his eyes off the spy to make sure the kids obeyed. The woman was screaming hysterically.
The spy was holding the woman with his left arm but as that arm lost blood, it got weaker. The woman managed to break free and the spy fumbled to keep his grip. When Mark could get a clear shot, he fired. The spy lay on the ground bleeding but not dead.
Mark approached carefully to see if the spy was truly down. He noticed a container that was oozing a strange metallic substance. The ooze seemed to be growing. It quickly consumed the spy. Mark was so aghast that it paralyzed him. Then the ooze touched his shoe and Mark ran. He called for Hazmat.
Where the ooze touched his foot felt weird. It didn't hurt but it felt like his flesh was crawling, literally. It felt like his toes were moving around inside his shoe and his foot was changing shape. Mark tried to wipe the ooze off but it had already been absorbed into his skin. The ooze ate his shoe and sock away. The ooze was moving up his leg when Hazmat arrived.
Mark noticed that this wasn't the usual Hazmat guys the FBI dealt with but considering his condition, he was willing to get help from anyone. The area was cordoned off. Mark couldn't tell if the woman or children had escaped. It did seem like there were a few others covered in ooze. Even the Hazmat people were not safe. Their suits didn't protect them from the ooze. However, most of the Hazmat seemed to know what they were dealing with and they collected the ooze with special vacuums.
Finally, they were able to put Mark on a stretcher. "Is the ooze gone."
"No, but it's stopped replicating. This means you're no longer contagious and it's safe for us to move you."
Mark saw the spy on a nearby stretcher. There wasn't much left of him. The spy was nothing but bones, a face, and a few bits of random flesh. The bones themselves weren't even human anymore. The spy looked dead. Mark feared that he'd wind up the same.
He looked closer at his leg. The ooze had now reached his crotch and was spreading up his torso and down the other leg. The leg that the ooze touched first had grown skinnier and longer. Instead of a foot, Mark now had what looked like a hoof.
"Are you sure this has stopped replicating?"
"Yes, but it is still active. I would say that the nanites inside you have calibrated together. That means that instead of working against each other like they did in that guy, your nanites have come to an agreement on what to change you into."
"Nanites? Change me into?"
"Yes, and from the looks of your hoof, you're going to be a fine pony."
"I don't want to be a pony. You have to do something."
"Unfortunately, there isn't much I can do. If I try to interfere with the nanites at this stage, they could rip you to pieces instead of restore you. Excuse me, I need to check on the others. I think you'll be fine."
Mark laid there watching his body slowly turn into a pony. Both legs were now pony legs. His pants had been absorbed and his shirt was being absorbed.
Someone came up to him with a bag of oats. "You need to eat all of this."
"That's 40 pounds. I can't eat that much."
"You'll have to eat 400 pounds unless you want to be a miniature pony. Don't worry, the nanites will adjust your digestion for you."
The guy brought over nine more bags of oats and left. Mark tried his best to eat the oats but they were too dry. He had a pile sitting on his chest and noticed his skin absorbed the oats so that's how he ate.
His chest began growing into a big barrel shape and his arms started changing. He could no longer use his hands and he cried for help. The guy who brought the oats came back and started feeding him.
As Mark's neck started to change, Mark asked, "Is this going to change my brain too? Will I stop being a human?"
"Your brain will be partially transformed. You need that so your brain can interact with your body. However, your memory and the higher functioning centers of your brain will be unchanged. Doctor Downway was toying with this idea for creating a way for someone to go undercover as a horse but no one else liked the idea. It looks like we're going to get ourselves a talking horse anyway."
As Mark's jaw began to change, it got harder to talk. "You sure I'll still be able to talk?"
"You'll have to relearn how since you're mouth will be different."
Mark tried to ask more questions but it was too difficult. His vision started changing as his eyes moved away from each other. The tampering with his brain caused him to pass out.