Katherine sighed as she tried to concentrate on her English work. It was no use, if she wasn't thinking about Boyd's death, she would be thinking of Ms Blake and Derek, or her and Aiden. How did everything turn out so wrong? She was brought out of her thoughts when Stiles and Scott turned around to look at her smugly.

"What now?" She said, rolling her eyes.

"I need to talk to Ethan...and I figured you might be able to get Aiden away from him for a few minutes?" Scott questioned.

"You want me to make out with him in Coach's office?" She sighed.

"That would be good" Scott admitted.

"Ugh, fine. Ms Blake, I need to go to the bathroom?" Katherine shouted out.

"Alright, don't take too long or you'll miss the test" Ms Blake replied.

"You both owe me" Katherine told Stiles and Scott and she got up from her seat and went to find Aiden.

She soon spotted him and grabbed his hand pulling him into Coach's office. Then she started softly kissing him, peppering them down his neck. She raised her arms out to pull his shirt of when he saw the way he was looking at her.

"What's that look for?" She asked.

"It's just...you haven't even spoken to me since..." He trailed off.

"Since your pack killed Boyd?" She stated.

"There was nothing I could do Katherine! I'm not strong enough to go up against Kali and Deucalion" He admitted.

"I know, I know...I'm just upset" She replied.

"Well then we shouldn't be doing this, I don't want you regretting things later" Aiden told her.

"Who knew you were such a gentleman?" She joked.

"Shut up and give me a hug" He sighed, pulling her close to him and she laid her head on his shoulder.

Suddenly a loud screeching noise broke them from their hold and they both looked to the door to see the werewolves sign for vendetta.

"Who?..." Katherine trailed off.

"Derek" Aiden growled, pushing open the door.

"Where are you?!" Aiden shouted.

"Aiden, stop!" Katherine told him.

"You want to fight Derek, come and get me?" He screamed.

Suddenly Aiden was pushed into one of the lockers and Katherine gasped when she realised that it was Cora who was fighting him. She started slashing at his chest, wildly.

"Stop it! Stop it!" Katherine repeated.

Quickly Aiden got the upper hand, grabbing Cora's wrist and slamming her into the wall, her head making a cracking sound. Aiden stalked towards Cora, claws out when Katherine pushed herself in between the two, grabbing Aiden's shoulders.

"Aiden, Aiden! Look at me! What are you doing?" She questioned as he finally started to calm down.

"I...she came at me" He insisted, as Ethan, Stiles, Scott and Lydia ran into the changing rooms.

"What did you do?" Stiles shouted.

"I didn't do anything" He replied.

"Yeah? Well she's not looking great, brother" Ethan exclaimed.

"She attacked me, I had to get her off me" He insisted.

"C'mon, let's go" Ethan suggested, pulling his brother away from the scene.

"Katherine..." He trailed off, not sure what to say.

After they had helped Cora up, she had insisted she was fine, but Katherine wasn't taking no for an answer and started cleaning a small scratch on her head.

"It's fine" Cora grumbled.

"It's not fine, until I say it is" Katherine retorted.

"Do you want me to call your brother? I'm sure he'll come pick you up" Katherine asked her.

"...Yeah, thanks Katherine" Cora said, giving her a small smile.

"That's alright. I'll just go outside so I can get some signal" She told her, walking out of the fire exit.

She took her phone out of her bag and dialled Derek's number.

"Katherine? Is something wrong?" Derek asked from the other side of the line.

"It's nothing serious, but Cora got in a fight with Aiden" She admitted.

"What happened?!" He questioned.

"I don't know, she just came at him claws out, and then when he threw her off him she hit her head. I think she's probably got a concussion" She explained.

"Where is she?" Derek said, coming up from behind her.

"What...how did you get here so fast?" She inquired.

"I was already at the school" He admitted.

"Why-oh. Nice" Katherine sighed.

"Are you sure Cora's alright?" Derek asked.

"Yeah, I think so, she's just inside" Katherine said, holding the door open for Derek.

"C'mon, you're coming home, now" Derek sighed, hauling Cora off to his car.

Later that day Katherine had decided to stay at the school to watch the music recital. Everyone knew something bad was going to happen, but they just weren't sure what it would be.

"Hey? You okay?" Scott asked as he and Lydia walked over to her.

"Yeah, I'm just worried...something really bad is going to happen and unless we figure out what it is..." She trailed off.

"We'll do what we can" Scott comforted her.

"I know" She replied, patting him on the shoulder.

Suddenly her phone vibrated and she saw she had a text from Aiden.

Need to talk to you...life or death. Meet in classroom 3A-Aiden

She looked over to the front of the hall and saw him staring at her, obviously concerned about something.

"What's wrong?" Lydia asked.

"It's Aiden, he says he needs to speak with me, life or death" She explained.

"Do you want me to come with you?" Scott questioned.

"No, it's okay. You need to stay here" She told them.

"Alright, be careful" Scott replied.

She quickly walked through the school's hallways until she came to classroom 3A. She knew something was wrong instantly. There was a strange smell coming from the classroom and she couldn't hear Aiden anywhere. Worried that he was hurt she entered.

"Aiden? You in here?" She cried out.

She whipped her head around when she started to hear a weird chanting coming from the hall. Figuring Aiden must have left she went to open the door and was surprised to find it was locked. Suddenly she saw a figure coming out of the shadows and sighed when she realised who it was, seeing she had a knife in her hands.

"...It's you isn't it?" She asked.

"I'm surprised you didn't figure it out sooner" Ms Blake smirked.

"Well who would have believed me" She admitted.

"True" Ms Blake stated.

"So, what is this? Another sacrifice?" She questioned.

"No, I have someone else in mind. You are more of a bargaining chip" Ms Blake explained, hitting Katherine in the head with the knife.

She fell to the ground, injured. She tried opening her eyes, but they just flickered in and out of focus.

"Why...why are you...doing this?" She mumbled.

"Because for some reason a lot of people seem to care about you" Ms Blake told her.

"What...are you going to do with...me?" She stuttered.

"Don't worry; I'm not going to kill you. Not yet anyway" She exclaimed and started chanting some sort of weird spell.

Katherine felt herself growing more tired and found she couldn't keep her eyes open.

"Derek..." She trailed off as she fell unconscious.

Later on, after Ms Blake had tried to sacrifice Lydia and had taken Stile's dad instead they found Katherine in one corner of the dark room.

"Oh my God! Is she okay?" Scott asked as he and Stiles bent down beside her.

"I think so. She's breathing" Stiles said, feeling her pulse.

"Katherine? Hey, can you hear me? Katherine?" He repeated, growing more anxious.

"She looks sick" Lydia stated from behind them.

"But...werewolves can't get sick" Stiles explained, confused.

"We should get her to the hospital. They might know what to do" Scott told them as he picked her up.

Once they arrived at the hospital the doctors checked her over and cleaned her wound.

"What's wrong with her?" Stiles asked them.

"We're not really sure. It's like her life force is being drained..." One of the doctor's trailed off, leaving the room.

"She'll be okay Stiles. She's Katherine" Scott insisted.

"What if she's not? What if my dad's not? I can't lose them Scott" Stiles admitted, a tear rolling down his face.

"She's strong and so is your dad...but we need to go Stiles if we want to save them" Scott explained.

Derek was reading a book when he got the phone call from Peter.

"Derek, you need to get to the hospital right away. It's Katherine" Peter told him.

That was all he needed to hear before he got into his car and sped off to the hospital.

When he got there he found Peter nowhere to be found but soon found Scott's mum.

"You're here about Katherine?" She suggested.

"Yes, where is she?" He urged.

"This way. We're not sure what's wrong with her Derek, but...it's not looking too good" She admitted, opening the door to her room.

"I'll leave you two alone" She told him shutting the door.

He walked over to her bed slowly and sat down. She had a bandage over her head and looked even paler than usual. He looked to his side to hear her heart monitor beeping slowly. He picked up her cold hand between both of his and held it up to his face, praying that she would be okay. A while later she woke up, confused.

"...Derek?" She questioned.

"Hey. Hey, I'm here" Derek said, standing up.

"What's going on?" She mumbled.

"We don't really know...you were attacked by someone" Derek admitted.

"Oh my God, the Darach!" Katherine realised.

"What? It was the Darach that attacked you?" He asked.

"Derek, I know who the Darach is...but you're not going to like it" She told him.

"Who?" He questioned.

"It's Jennifer...I'm sorry Derek" She sighed.

"I...she did this?" He inquired, sitting back down in shock.

"Yeah" Katherine stated.

"Guess you're going to tell me I told you so then" Derek sighed.

"No I'm not...but you need to go find her. You'll be the first person she goes to" Katherine explained.

"No! I'm not leaving you" He argued.

"Then more people are going to die" She replied.

"I'm not going...she might come back to hurt you" He insisted.

"Please Derek...just get someone else to stay?" She suggested.

"Alright...I'll call Peter" He told her, picking up his phone.

"Peter I need you to get to the hospital. ASAP" Derek ordered.

"Well that's good then nephew, because I'm already here" Peter said, walking through the door.

"I was the one who called you about Katherine remember?" He continued.

"How'd you know?" Derek inquired.

"I have my sources. Now go, you need to find the Darach" Peter insisted.

"Alright but if you hurt her-" Derek was cut off.

"I don't know if you've realised yet nephew but I do actually care about this girl" Peter admitted.

"Why?" Derek asked.

"Because you do" Peter explained.

"I'll be back as soon as possible, protect her with your life" Derek told him, quickly kissing Katherine on the forehead and walking out of the room.

Scott and Stiles had realised that the first place Ms Blake would go is to Derek's loft, so they stormed over there as soon as possible.

"Where is she? Is she here?!" Stiles shouted.

"Who?" Derek asked.

"That bitch, Ms Blake" Stiles answered.

"You know?" Derek questioned.

"Yes we...wait how do you know?" Stiles asked.

"Peter told me she was at the hospital and she explained what had happened" Derek told them.

"She was awake?" Scott questioned.

"Yes, for a bit" Derek stated.

"Derek, we need your help" Scott explained.

"I'll do whatever you want me to" Derek told him.

It wasn't long before Ms Blake showed up, expecting Derek to welcome her with open arms.

"Derek? Are you here?" She called out.

"I'm here" He said from behind her.

"Oh Derek, something's happened, people are-" She was cut off by Derek putting a clawed hand up.

"...Their already here, aren't they?" She continued, seeing Scott and Stiles come out of the shadows.

"We told him you're the one killing people" Scott told her.

"Oh that's right? Committing human sacrifices? Cutting people's throats? Yeah, I probably do that in my lunch hour. That way I can get back to teaching high school English for the rest of the day. That makes perfect sense" She insisted.

"Where's my dad?" Stiles cried.

"How should I know? C'mon Derek, you can't believe this?" She questioned.

"Do you know what happened to Stiles father?" He replied.

"No" She stated.

"Ask her what she's done to Katherine?" Scott inquired.

"Katherine? I don't know anything about that" She told them.

"Well then what do you know?" Derek shouted.

"I know that these boys, for whatever reason are filling your head with ridiculous stories. And one they can't prove" She insisted.

"What if we can?" Scott suggested, taking a bag out of his pocket.

"What is that?" Ms Blake questioned.

"My boss told me...it's a poison and a cure. Which means you can use it...and it can be used against you" Scott explained, throwing the substance at her.

She instantly started to change, her face becoming discoloured and scars appearing. She didn't even look human. She soon changed back, angry.

"Mistletoe?" She inquired.

Suddenly Derek grabbed her by the neck and took her off the ground, strangling her.

"Derek!...Wait, wait. You need me" She insisted.

"What are you?" He snarled.

"The only person who can save Katherine" She told him.

He let her body drop to the ground.

"Who's with her now?" She asked them.

"Peter" Derek admitted.

"What? What's Peter doing there?" Scott asked.

"He heard what had happened. Believe it or not, but I think he does actually care about Katherine" Derek explained.

"Call him!" She ordered.

"It's not good. She's in and out of consciousness. She's vomiting up black blood with one other alarming substance" Peter told him.

"Mistletoe" Derek realised.

"How'd you know that?" Peter asked as Derek hung up, grabbing Ms Blake's neck again and squeezing it.

"Derek! Derek, what are you doing?" Scott shouted.

"Her life...it's in my hands" Ms Blake stuttered; only making Derek's grip grow stronger.

"Derek, stop!" Stiles shouted.

"Stilinski, you'll never find your dad...and your best friend will die" Ms Blake taunted.

"Derek! Derek!" Scott screamed as Derek finally let her go.

"That's right, you need me all of you" Ms Blake smirked.

"Why? Why her of all people?" Derek asked, as they got into the car.

"Because I know how much you care about her, you'd do anything for her, and I need you to do anything I ask" She explained.

Meanwhile back at the hospital Katherine wasn't getting any better and had now picked up a fever. Peter was frantically trying to cool her down by putting a cold cloth on her head.

"C'mon Katherine, if something happens to you while I'm here, I'm dead. You don't want Derek to kill me do you?" Peter joked, hoping Katherine could hear him.

"Hey, anyone want to tell me when they're getting my friend out of here?" Peter shouted as a doctor ran past him.

"Sorry, but she wasn't...uh...you're supposed to be dead" Melissa said in shock when she saw him.

"I get that a lot actually" Peter replied.

Suddenly Katherine's eyes opened and she sat up, puking up more black blood.

"What's wrong with her?" Melissa asked.

"We don't know" Peter admitted, worried.

Author's Notes: Hope you guys enjoyed this chapter, sorry it's a bit short! Also you might have noticed I mixed a few scenes from episode 3x10 in here because I thought they made more sense, so I hope that didn't confuse people:) And yes I have also changed Katherine being the one who's sick rather than Cora because I never really understood how Cora got hurt in the first place etc and there are going to be some cute scenes coming up with her and Derek because of it;) Send me any messages or reviews you have! Next chapter is based on 3x10!