A/N: this story will probably lead to Alec/OC. I'm sorry, but I'm not a huge Malec fan. This will also be partial AU, because I made Magnus leave because of trouble with the Clave (being accused of practicing black magic), I made Alec (eventually) straight, and this will be without COFA. It will be if the series ended after COG. I do not own any characters mentioned, except for the nameless (for now) girl. I don't own the Mortal Instruments. If I did, I would be doing some HIGHLY illegal things to either Jace or Alec.

Alec POV

Everyone was hanging out in the library, as usual, when Mom walked in. "Alec, Isabelle, there is a Du'sien demon nearby. It should be a few minutes out of town." Izzy, Jace, and I all got up. "Not you, Jace. You still need time to recover after your battle with Sebastian and Valentine."

Of course, Jace being Jace, he started to complain. "Come on, Maryse! I'm fully recovered. It's been two weeks! I'm fine. See?" he started flexing and giving his arrogant smile.

She wouldn't budge. "No. I'm not going to let you put yourself in danger when you just got out of the infirmary last week. And it's only one Du'sien. Besides, consider this time off to finally be alone with Clary since now you know you're not related."

We put on our gear, I got my bow and arrows, a Sensor, and a few seraph blades, and my sister and I were ready to go.

…..

We eventually tracked it down to an abandoned one-story building that was the epitome of 'spooky', and this was coming from a Shadowhunter. Izzy took the upstairs, and I took the basement. Suddenly, I heard something. It sounded like a strange mix between hyperventilation and crying. The voice sounded female. What was going on? It came from the end of a corridor with about five other rooms, and the smell was awful, like decaying flesh mixed with blood, vomit, mold, and dirt. What was going on down here? I opened the door.

Upon first glance, the room seemed empty, except for a girl's voice crying and saying something in Latin. Why did I have to fall asleep during ancient languages class? I caught the word, "Valentine" and listening closer, I made out "no more tests". I took out my witchlight and saw the girl. She was Izzy's age and Jace's height, I imagined, with pitch black hair that reached past her waist and sunken dark gray eyes. She was wearing black sweatpants and a gray long-sleeved t-shirt and was barefoot. She might have been pretty if she was not so painfully thin.

I ran over to her before she would hurt herself or me. I put my hands on her shoulders and shushed her. "I'm not Valentine. I won't hurt you."

After I said I wasn't Valentine, her eyes widened as she struggled to get away from me. "You're Jonathan, then." It wasn't a question. How did she know about Jonathan? She yelled, "I won't let you take me!"

Out of the corner of my eye, I saw Izzy come in, and judging by the fact that her necklace wasn't glowing anymore, she killed the demon. She stayed silent. "No, I'm not Jonathan, either. Valentine and Jonathan are dead. I'm Alec Lightwood." I pointed to my sister. "This is my younger sister Isabelle." She relaxed a little, before she started coughing, then realized in horror that she was coughing up blood. She fainted from the blood loss.

Izzy finally spoke up. "Roll up her sleeves and check for Marks, Alec. She might be one of us." I did just that. Her hands had the open eye rune on both of them. When I rolled her sleeves up further, her skin was covered with the scars of faded runes and the insides of her elbows were covered with little marks, as if poked with a syringe.

"She's definitely one of us. I just want to know who she is. Let's take her back to the Institute