A/N: Written for Ectober Week 2018, combining the prompts for Day 26 (Disappearance) with Day 28 (Corruption). Standard disclaimers apply.

Jazz had been noticing it for a while, but she couldn't quite put her finger on what it was. It seemed to be more a gut feeling than anything else. An accumulated number of observations that were easily explained away when looked at individually.

Small things.

Tiny things.

Hardly significant things.

Danny had been avoiding Jack Fenton more and more, which wasn't terribly surprising given that Jack seemed more and more enthusiastic about showing off his latest inventions. Even Jazz had had to dodge more than one blast this week, and it was only Wednesday. Danny's English mark had marginally improved, mostly likely because his training with Sam and Tucker (and her, when he let her join) was finally paying off and he was a little bit faster at catching invading ghosts than before. His powers had certainly gotten stronger and more precise.

But then there were the things that didn't make quite as much sense.

He'd only taken one cookie the day Maddie had baked his favourite, when in the past she'd had to fight to get even one for herself between him and Jack.

He'd missed a golden opportunity to make fun of her for still caring so much about Bearbert Einstein.

He still got angry at her when she mothered him, complaining that she was interfering, but it wasn't as much tease as truth anymore. He was colder towards her, more distant than he'd ever been since she'd discovered his secret. Her efforts to remedy their relationship—including apologizing for whatever she'd done, since she had no idea what it was—hadn't borne fruit.

She'd finally asked Sam and Tucker, only to be told that Danny had been crankier than usual, probably because he was getting less sleep, and that it would blow over. He was rarely like this, and when he was, it was never for long. It was nothing to worry about.

She might have believed that, if it didn't belie what she knew was true.

Jazz stood in front of Danny's bedroom door, weighing the merits of being polite and knocking against barging in and actually getting some answers. When faced with this dilemma in the past—heck, when faced with this dilemma last week—she'd decided it would be best to knock. To respect his privacy. Their bedroom doors didn't lock, and she knew how much he had on his plate.

But he still wasn't telling her anything, wasn't even telling Sam and Tucker as far as she could tell, and—

Jazz decided on the best sibling move: go right in for her brother's sake and apologize later. She took a breath, turned the knob, and pushed.

Danny's eyes found hers immediately. He was sitting on the side of his bed, with...something in one hand. A needle? Yes, a needle, a big one, full of something glowing and green and— "Is that ectoplasm?"

"Shut the door!"

Whatever this was, it wasn't normal. Jazz swung out one foot, caught the door, and kicked it closed. Danny looked almost disappointed. "You were going to disappear once I turned my back, weren't you?"

"This isn't any of your business."

"Well, then I'm going to make it my business because you're my little brother and I care about you. So spill."

He stared at her.

Frowned.

Shoved the needle under his pillow, as if that would make her forget about it. Scooted closer to the head of the bed, as much to protect whatever that was supposed to be as to give her room to sit if she so chose.

At this point, she'd rather tower over him and glower until he gave her answers.

It didn't take him long to cave and break the silence. "You aren't supposed to know. I shouldn't tell you."

"Shouldn't tell me what?"

"To be fair," he continued, ignoring her, "I don't think I'm supposed to know, but something went wrong."

"Danny?"

He stared at his hands before finally whispering, "I got corrupted. Still am corrupted, even with the stabilizing solution I found in the basement."

Jazz swallowed. She had no idea what he was talking about. "Danny?" she repeated hesitantly. "What are you—?"

"I don't know the whole story. Obviously. It's dangerous for me to know the whole story. So I can't tell it to you."

"Then what can you tell me?"

He finally raised his head to look at her. "You're the smartest kid in school, Jazz. Should've made the cover of Genius Magazine all by yourself. Your work on ghost envy alone is ground-breaking, and you haven't even finished high school. Paranormal psychology might not take off, but you'll be brilliant in the field anyway. You're also annoying, overbearing, and overprotective, but you mean well. You help keep this family together, help keep everyone sane. Make sure we all get to eat healthy food that's not contaminated. You're there for me when Sam and Tucker can't be. Do you want me to keep going?"

"I…. I don't think I understand."

"No, you don't." He was entirely too calm for this conversation, in her opinion. She had no idea what she'd caught him at, and now— "It's really better if I keep it that way."

She sat down next to him. "Danny, you know I can keep a secret. If you've got something else on your plate now, please tell me. I might be able to help."

"It's not just my secret this time." He cocked his head at her. "And it's a secret that'll destroy you. Are you really sure you want to know?"

Something inside her tightened as dread settled over her. "I think I need to, especially if you believe that."

"Even though there isn't anything you can do about it?"

"I'd rather you let me be the judge of that," she said gently. "Now what's this about thinking you're corrupted?"

He shook his head. "Not thinking. I know I am. And that's why I know that I am, because I know. Because I remember everything."

"That doesn't make sense."

"Does too. You just don't know how to interpret it."

She closed her eyes. "Danny, please, I just want to help you."

"It might be too late for that." She looked at him again and cocked an eyebrow, waiting. He took the cue for what it was. "It's been weeks. Help probably isn't in the cards anymore. You didn't notice fast enough."

Now wasn't the time to point out that she'd felt something had been off for a while. "Notice what?" she said instead.

"Me." He jumped to his feet, walked in a circle around his room, and turned back to face her. "I can't help you. It's best that you forget this."

Jazz rolled her eyes. "I'm not about to forget this. At least tell me what that is, even if you won't explain anything else." She gestured to the pillow, not missing how his eyes tracked her hand in case she lunged for it.

Danny grimaced. "I thought it would stabilize the mutation. It hasn't. Not exactly."

"What mutation?" She couldn't stop her voice from climbing. "What are you talking about?"

"If I overdo it. Push my limits. It makes me weaker. I…. I start to break down. I thought a single dose would solve my problem. It hasn't, and now I've had to try to make it myself. I don't know if I've got the recipe right. Jack's notes are hard to read, and there's no guarantee everything's written down. At least it's not getting any worse. That's the good thing."

"Danny—"

"I can't ask for help. If I ask for help, he'll know I know. That's why I can't tell you. That's why I can't tell anyone."

Jazz narrowed her eyes. It wasn't hard to guess who he was talking about. "What does Vlad have on you?"

A strangled laugh escaped her brother. "Everything."

She crossed her arms and fixed him with a look that he knew very well. She could see him debating telling her, wrestling with his conscience and weighing the outcomes against each other. He had always had trouble hiding that kind of thing from her. "Danny?" she finally prompted, hoping it would break the dam.

He swallowed. "I owe him my life."

Jazz snorted. "Come on, little brother. If anything, that'll be repayment after you saved his skin. Wasn't the whole Pariah Dark thing his fault?"

Danny shook his head. "No. I mean, that might be, but, uh, that's not what I mean."

"Then do enlighten me."

He rubbed the back of his neck. "I don't know how I should put this. It's kinda hard to hear."

She sighed. "I promise not to freak out over the fact that you put yourself in a life-and-death situation again and didn't tell me, okay? Not overly, at any rate. Because you are going to tell me now, and I can accept that it might have been hard for you not to tell me earlier."

"It's not…." He trailed off. Swallowed. "I'm, ah, not exactly who you think I am."

She wasn't in the mood to play games. "Meaning?"

"I'm…I'm not your brother."

Wait.

What?

Jazz's eyebrows shot up. "What are you talking about?"

"I'm not your brother," he repeated.

The got her to her feet. "Then who are you?" she growled, striding forward to face him down even though—as a ghost—he'd be able to do a lot of damage to her if he wanted to. She was lucky he seemed fairly benign. He was lucky she didn't have any weapons on her. "You know what? I don't care who you are. Just get out of him. Let him come back."

"I'm not possessing him. I'm me."

"Fine, then you're impersonating him. So who are you? Amorpho? After you apparently promised to never come back?" Danny had filled her in. Warned her. And now she still hadn't realized. Some sister she was.

He shook his head. "I don't know how to shapeshift."

"Then what—"

"I'm like Danielle!" he burst out, stepping away from her.

That stopped her short. "Who's Danielle?"

The ghost who definitely wasn't her brother looked shocked. "He never told you?"

"I'm going to kill him," she muttered. As soon as she found him. She'd hug him so hard she'd squeeze him to death. "No. He never told me. So you tell me."

"Danielle and I aren't the first," he said slowly, "but we're the most successful ones. So far. I expect experiments are continuing…."

She glared even as his voice died to nothing. "Experiments?" It had to be Vlad. She didn't need him to confirm it any more than he already had. It wasn't their parents, and no one else—!

The imposter walked over to Danny's desk and picked up a pair of scissors. Jazz didn't try to stop him as he used one blade to make a small cut on his left pinky and held it up for her inspection. "I still bleed," he said, "but ectoplasm in my DNA isn't balanced. It's not, I dunno, bonded properly. When I use my powers, it breaks down. And I start to lose my form."

He wasn't answering her questions, not really, but she could read between the lines. She knew how Vlad had fixated on her brother and her mother. She had a good idea what had happened to Danny during the accident, knew that Vlad had gone through something similar. This imposter had been subjected to the like, something that didn't take, except—

He let a small ghost light glow in his open hand, and as she watched, his fingers began to glisten. Green began to bubble from the wound as the skin on his fingers threatened to droop and drip like wax—

He closed his hand, cutting off the light. Ectoplasm and blood stained his skin when he opened it again. He pointed toward the hidden needle. "It'll help," he said as she reluctantly unearthed it.

He took the needle from her with his good hand, lifted his shirt, and jabbed it into his stomach without seeming to care where. She grimaced. "I don't think—"

"It's fine." He tossed the needle into the trash can and wiggled the fingers on his left hand; they looked normal again. She wasn't in the mood to scold him about using the sharps discard right now, not when that would take this conversation down to the lab. Not when it would mean this conversation was over. "This isn't the first time I've had to do this."

She took a slow breath. "How long?"

He didn't blink. "I've been active for three months, here for just over half of that."

"Then Danny—?"

"I don't know. I wasn't told. I'm not supposed to know, remember? The programming phase was supposed to be wiped from my memory. I was supposed to come here and think I was your brother. But I don't. I remember everything." Silence for a moment; she was too shocked to fill it. "I wish I didn't. I want to be my own person."

She moved back to his bed and sat down, trying to convince the contents of her stomach that she didn't need to see them again. She'd never known Vlad had gone this far, never known how many lines he'd been willing to cross. She'd never wanted to think about it, but she couldn't deny the evidence in front of her.

Human experimentation.

Cloning.

Kidnapping.

Replacement.

"Why go along with this at all?" she whispered. "If you don't want this, either?"

"Because I don't want to die," he answered simply. "And even if I don't, if he finds out that I remember…. I'll have to go through it again. And I can't."

Jazz had seen Danny in pain before.

Even knowing the boy with his face wasn't her brother, her heart still twisted at the haunted look that crossed his face.

"Then we work together," she said. "To get Danny back. To get you a new life. Away from Vlad."

"Like Danielle?"

"Like Danielle," she agreed, though she had no idea what sort of life this Danielle led. "Will you help me?"

He dropped his gaze to his feet. "What if it's too late?"

"It's not." It can't be. "Vlad would have made some sort of move if it were. Wherever Danny is, he's fighting."

"And if we can't find him?"

"We'll find him. If nothing else, the Booo-merang—"

"It'll get confused with my ecto-signature. It's too similar to his."

"Then we refine its sensitivity," she said, even though she wasn't sure how to do that. Tucker might. She'd have to ask. They'd want to help get their friend back, too. "We'll figure it out. We'll get Danny back. We'll get you away from Vlad. You can have your own life. Find out…find out who you really are."

"I'd like that," he said quietly.

"Good. Then we'll make it happen." She jumped back to her feet. She needed to do something, needed to fix this, needed to help her brother. "First things first. If we're working together, I need to call you something. Something besides Danny."

Silence for a moment. Then, "Call me Daniel. That's who I was made to be. It'll do until I'm free."

"Daniel then." Jazz stuck out her hand, giving him a pointed look until he tentatively reached out and took it. She gave it a firm shake. "You can still call me Jazz. Because we're friends and partners." No use holding a grudge. It wouldn't help any of them. "And we're going to get to the bottom of this and get Danny back. Now, tell me everything you remember."