Katherine was already twelve steps ahead of Derek. While he carefully guarded the cabin where he lived to make sure nobody came near, she had been getting in touch with her people. Derek would occasionally catch snippets of these conversations with his enhanced werewolf hearing. He had the feeling that Katherine was someone that people couldn't say no to. Yet she didn't rule by destruction like Klaus did, no she killed with kindness. Which wasn't to say that Katherine was always kind, it was just that she had a manner about her that made people want to do exactly what she told them to. Derek was actually a bit envious of how easily she managed her little web of soldiers.
It was then that Derek began to realize that he was going to need his own army. Klaus had one before they were all killed. Katherine had one. She had been the one who told Derek that he would need an army to destroy Klaus. If that was true then he would start making himself one. He never thought he would ever have a pack again. Laura had been his pack and when Klaus had killed her, his last remaining relative that feeling of being connected had left Derek. He hadn't bothered trying to get close to anyone ever again but he could feel Katherine breaking down his walls. He was so close to the revenge that he had been craving he could almost taste it.
Derek wasn't going to just go find someone and randomly give them the bite. He didn't want to turn anybody into a wolf without their consent. Which meant he needed to find someone who wanted that kind of burden. It wasn't that hard to break into the town doctor's office and begin going through the files. Being turned into a wolf would cure most diseases that plagued humans. The bite could be a gift for some and it didn't take Derek long to find the first member of his new pack. She was a young pretty blonde or at least she would be pretty if she put some effort into her appearance. Then again it was probably hard to find the motivation to primp when at any minute you might drop the floor and piss your pants. Poor kid. She just looked so wounded that Derek felt something kindred in her. She spoke to some deep protective part of himself.
He followed Erica for awhile, getting used to her daily routines. It was summer vacation which meant no school and since Erica didn't have any friends she spent most of her time at home alone while her parents worked. She was home alone and Derek was standing outside in the dark, staring up at her window. He watched, confused when she walked out onto the roof. He couldn't quite see what she was doing up there, maybe she had gone to fetch something but Derek smelled sorrow on her.
In an instant he sprang into action and leaped over several shrubs in the well manicured lawn. He was underneath Erica, catching her easily in his arms before she could hit the ground. She was still seizing so he held onto her tightly as he let himself into her house. He doubted that her parents would be home for awhile. He carried her upstairs to her bedroom and sat down on the edge of her bed until she finally stopped and then she laid her down gently on the bed.
"Were you trying to die?" he asked after several minutes of silence.