A/N: This is a multi-chaptered fic which I have already written most of. I will aim to post 2 chapters a week (on a Saturday night) as they are not very long.

Basically, the premise of this fic is 'what if Izzy was Valentine's daughter too?' My basis for this idea is the combination of several odd details in TMI: Izzy's eyes are described as being 'very dark' and 'almost black' – Maryse has blue eyes, Robert has blue eyes, blue eyes are a recessive allele so IGCSE Biology suggest to me that they must both be homozygous for the blue-eye allele, therefore Izzy should be too (I am aware that my science here is over-simplified and there are more complex loopholes that explain her eye colour away – but combined with the other things I think it contributes to a sound argument)…who else has 'black' eyes? Valentine. He refers to Maryse as 'my Maryse' Now, he may be referring simply to her being a key member of The Circle…but he doesn't address Luke as 'my Lucian' or Robert as 'my Robert'. There is also the fact that at the end of 'City of Lost Souls' Maryse recognises the echo of Valentine's handwriting in Johnathon/Sebastian's. The Circle met all the time, were together all the time, Valentine didn't need to send them letters – certainly not enough letters for them to become intimately familiar with his handwriting. Even if the others would have recognised a sample of Valentine's handwriting, they wouldn't have known it well enough to see the similarities in his son's penmanship – that is the recognition of someone who has studied his writing (who has received many letters and read them repeatedly…love letters?). We know how unhappily married Maryse and Robert were. Robert was distracted by the deterioration of his relationship with Michael and own increasingly unwilling involvement in The Circle. Jocelyn was plotting her betrayal and Valentine sensed or suspected this…it would have been only too easy for Maryse, arguably the most devoted of all of them – to him, to the cause – to find comfort in his arms and for Valentine to take reciprocal comfort in hers and/or use the relationship to cement her loyalty and emotionally manipulate her…

I genuinely think Izzy is Valentine's daughter in the subtext of canon. This fic will explore what could have happened if Valentine had realised the truth.

It begins in CoA and continues through CoG. Because it's only slightly AU, what I have done is rewritten scenes that would have changed and added in extra scenes as necessary. If you know the books well, it should be obvious where the scenes fit into and/or alter the original narrative. Let me know if it's too confusing and I'll post summaries of what has happened prior to the start of each chapter to provide context. Thank you very much for reading and I really hope you like it!

'She wasn't looking for a knight; she was looking for a sword.'

'Blood doesn't equal love.'

Chapter 1 - Sins of the Father

Trigger Warnings: (tbh I'm not sure this chapter needs any but better safe than sorry) allusions to/implied child abuse, blackmail, discussion of child endangerment, allusions to/implied emotionally abusive relationship.

Jace's father was a formidable man, over six feet tall with a wide chest and hard, thick arms corded with ropy muscles. His face was almost triangular, sharpening to a hard, pointed chin. He might have been considered handsome, Alec thought, but he was startlingly unlike Jace, lacking anything of his son's pale-gold god looks. The hilt of a sword was visible just over his left shoulder – the Mortal Sword. It wasn't as if he needed to be armed, since he wasn't corporeally present, so he must have worn it to annoy the Inquisitor. Not that she needed to be more annoyed than she was.

"Imogen," Valentine said, his dark eyes grazing the Inquisitor with a look of satisfied amusement. That's Jace all over, that look, Alec thought. "And Maryse, my Maryse – it has been a long time." There was a weight and an edge to his tone that Alec did not quite understand, but the possessive words chilled him; Maryse was independent to the point of being distant even with her family and he couldn't imagine her belonging to someone the way Valentine seemed to be suggesting she had.

Maryse, swallowing hard, said with some difficulty, "I'm not your Maryse, Valentine. Not anymore."

"And these must be your children," Valentine went on as if she hadn't spoken. His eyes came to rest on Isabelle and Alec. A faint shiver went through Alec, as if something had plucked at his nerves. Jace's father's words were perfectly ordinary, even polite, but there was something in his blank and predatory gaze that compelled Alec to step in front of his sister and block her from Valentine's view. He thought he might have seen a flicker of cold amusement in the man's black eyes, but his strong features remained so totally impassive it was hard to tell. "They look just like you."

"Leave my children out of this, Valentine," Maryse said, clearly struggling to keep her voice steady.

"Well, that hardly seems fair," Valentine said, "considering you haven't left my child out of this. "He turned to the Inquisitor. "I got your message. Surely that's not the best you can do?"

She hadn't moved; now she blinked slowly, like a lizard. "I hope the terms of my offer were perfectly clear."

"My son in return for the Mortal Instruments. That was it, correct? Otherwise you'll kill him."

"Kill him?" Isabelle echoed, her words a perfect mirror for Alec's thoughts. "MOM!"

"Isabelle," Maryse said tightly, as Valentine's eyes flicked briefly back to her daughter. "Shut up."

Isabelle opened her mouth to protest further. Alec didn't blame her, but there had been such urgent tension in their mother's voice that he squeezed Isabelle's hand in silent warning and she closed her mouth accordingly, directing a resentful look at him even as she complied with his unspoken instruction.

The Inquisitor shot Isabelle and Alec a venomous glare between her slitted eyelids. "You have the terms correct, Morgenstern."

"Then my answer is no."

"No?" The Inquisitor looked as if she'd taken a step forward on solid ground and it had collapsed under her feet. Alec was not even remotely as surprised as she seemed, but he still felt the monosyllable like a punch in the gut - one which you had anticipated without being able to dodge. It wasn't that he'd wanted Valentine to agree to the trade, the last thing he wanted was for Jace to be handed over to his so-called father (not that he could be, given he was no longer in the Malachi Configuration, but that was beside the point); it was just that seeing the man live down to his son's lowest expectations of him hurt Alec on his parabatai's behalf. There had been no bitterness in the younger boy's voice when he'd told them in Izzy's bedroom that Valentine would never go for the Inquisitor's plan, but there had been no doubt, either. He knew his life was not worth as much to his father as power was and Alec only now realised that some part of him had foolishly been hoping Valentine would prove Jace wrong – if only to break Jace of his conviction that adults couldn't be trusted and would all inevitably let him down. Alec should have known better than to expect that proof to come from the man who had instilled the mistrust in Jace in the first place. What sort of a parent cared more for glorified cutlery than his own child? That, Alec realised, was the crucial difference between Valentine and his own parents. Jace had spat out earlier that the only difference was the Lightwoods were caught and punished, but it wasn't true. The difference was that Maryse and Robert had abandoned a cause they were devoted to and surrendered to the scant mercy of the Clave because their son needed them, and that mattered more to them than all the ideology in the world.

The Inquisitor was floundering. "You can't bluff me, Valentine. I will do exactly as I threatened."

"Oh, I have no doubt in you, Imogen. You have always been a woman of single-minded and ruthless focus. I recognize these qualities in you because I possess them myself."

"I am nothing like you. I follow the Law—"

"Even when it instructs you to kill a boy still in his teens just to punish his father? This is not about the Law, Imogen, it is that you hate and blame me for the death of your son and this is your manner of recompensing me. It will make no difference. I will not give up the Mortal Instruments, not even for Johnathan."

His name is Jace, Alec thought, suddenly furious at the man who stood there and calmly stated that he would sacrifice his child for a sword and all the while called Alec's brother by a name he hated.

The Inquisitor simply stared at him. "But he's your son," she said. "Your child." She sounded incredulous and almost desperate. She suddenly seemed vulnerable; Alec had never wanted to shake someone more. He knows, you idiot. He just doesn't care. This is Valentine Morgenstern we're talking about. If you'd just listened to his son, to my mother, to someone who actually knows Valentine, you wouldn't be in this position. He wondered how someone so embittered could be so naïve.

"Children make their own choices," said Valentine. "That's something you never understood. I offered Johnathon safety if he stayed with me; he spurned it and returned to you, and you'll exact your revenge on him as I told him you would. You are nothing, Imogen," he finished, "if not predictable."

The Inquisitor didn't seem to notice the insult. "The Clave will insist on his death, should you not give me the Mortal Instruments," she said, like someone caught in a bad dream. It was exactly how Alec was beginning to feel. He knew she was right – the Clave would follow the letter of the Law, as they always did. Valentine's aim was the destruction of everything they stood for and they would retaliate by digging their heels in and proving their refusal to bend with a teenager's blood. Alec wasn't worried about Jace dying (well, no more than he always was), he and Izzy (and, he conceded, Clary) would never let that happen; it was just that he was beginning to see a lot of running and hiding in their future and being fugitives accused of treason was not how he had wanted things to go.

The Inquisitor still seemed to be reeling with the horror of the situation she had created. "I won't be able to stop them."

"I'm aware of that," said Valentine. "But there is nothing I can do. I offered him a chance. He didn't take it." His voice was unfeeling, unflinching, and Alec felt another chill. He couldn't imagine what it must have been like for Jace, being raised by someone who could talk so coolly about allowing his child to be murdered when it was in his power to prevent it.

"Bastard!" Isabelle shouted suddenly, and made as if to run forward; Alec grabbed her arm and dragged her backward, holding her there. "He's a dickhead," she hissed, then raised her voce, shouting at Valentine: "You're a dickhead!"

"Isabelle!" Alec covered his sister's mouth with his hand but couldn't help feeling a slight satisfaction at her crude but accurate declaration. It was exactly what he had been thinking and he almost wished Jace was there to hear Isabelle swearing at his father for him. His satisfaction faded rapidly into discomfort when Valentine, who had spared them both a single, amused glance, paused, his eyes lingering on Isabelle. He surveyed her searchingly for a moment, the derisive mirth on his face fading and distorting into an unidentifiable expression as he stared at her eyes – not making eye contact with her, as a normal person might have done, but fixing his penetrating gaze (that made Alec's skin prickle slightly all over, as though he were abruptly aware of every single hair on his body) on her dark, currently defiant, irises. Alec wrapped a protective arm around his younger sister's shoulders (although he kept his hand over her mouth in case she started hurling insults again), staring Valentine down when his eyes flicked fleetingly to him. There was something eerily familiar about his eyes, but Alec couldn't place what it was. He recognised them but they couldn't have been further removed from Jace's molten gold.

"Isabelle." Slowly, deliberately, Valentine turned to Maryse. "Not the name I would have chosen." Alec and Izzy looked between them, bemused, as Maryse sucked in a sharp breath but didn't reply. He continued softly, "She really does look just like you, except…" He didn't finish the sentence. Anybody else doing so would have seemed to trail off but Valentine Morgenstern was not the kind of man who trailed off. He had left it hanging intentionally, Alec was sure, though he himself did not understand why. His mother seemed to though, because regaining her voice she hissed, low and deadly, "Keep away from my children, Valentine."

The latter merely raised one eyebrow sardonically and, smoothing his features, seemingly effortlessly, back into an emotionless mask, turned again to the Inquisitor who seemed barely to have noticed the strange exchange, so consumed was she in the horror of what she had done. Isabelle glanced up at Alec questioningly but he merely shook his head, equally perplexed and trying not to let on how disconcerted he was.

"You…offered him…" The Inquisitor was starting to remind Alec of a robot whose circuits were shorting out. "And he turned you down?" She shook her head. Alec hoped the motion might also shake her senses or at least her composure back into place. "But he's your spy—your weapon—"

"Is that what you thought?" he said, with apparently genuine surprise, which, Alec thought, was not unreasonable really, because it had been a stupid thing to think; not because Valentine was above using his son in that way (and really, shouldn't the Inquisitor have known that a man she believed to be using his child as a weapon would be willing to sacrifice that same child on the altar of his cause?), but because his son was Jace. "I am hardly interested in spying out the secrets of the Clave. I'm only interested in its destruction, and to achieve that end I have far more powerful weapons in my arsenal than a boy."

"But—"

"Believe what you like," Valentine said with a shrug. "You are nothing, Imogen Herondale. The figurehead of a regime whose power is soon to be shattered, its rule ended. There is nothing you have to offer me that I could possibly want."

"Valentine!" The Inquisitor threw herself forward, as if she could stop him, catch at him, but her hands only went through him as if through water. With a look of supreme disgust, he stepped back and vanished.

Alec released his hold on Isabelle, half-expecting her to start screaming the moment he took his hand off her mouth. She didn't. She stood beside him and stared as the Inquisitor stood, swaying slightly, her face a chalky grey-white. Maryse didn't look much better. The rigid tension in her muscles, that had been holding her together ever since the projection of Valentine entered the room, drained away the instant he left, along with most of the blood from her already pale face. She staggered slightly and both her children moved to support her, but she had already righted herself, smoothing her hair unnecessarily and apparently unconsciously, as if to give her hands something to do other than tremble.

"Mom," Isabelle began tentatively "what did Valentine mean when—"

Maryse brushed her off "Not now, Isabelle." She gestured vaguely to the Inquisitor who was staring as though transfixed at the spot where Valentine had disappeared, looking helpless and pathetic; had Alec been less angry with the woman, he would probably have found the ruthless politician reduced to such a feeble mess to be a pitiful sight. He expected his sister to argue, but to his slight surprise she accepted their mother's dismissal, possibly agreeing with Alec's opinion that what Valentine would do now posed a more pressing problem than what strange things he had said about Izzy.

"Imogen," Maryse said. There was no feeling in her voice, not even any anger – as though she had experienced so many emotions in the last few minutes that she couldn't take anymore and so had shut feelings out entirely.

The Inquisitor didn't seem to hear her. Her expression didn't change as she sank bonelessly into Hodge's old chair. "My God," she said, staring down at the desk. "What have I done?"

Maryse glanced over at Isabelle. "Get your father."

Isabelle, looking as frightened as Alec had ever seen her, nodded and slipped out of the room.

Returning barely a few minutes later, in gear and having retrieved her beloved whip, Isabelle pushed her confusion and questions about the unnerving encounter with Valentine down and focused her mind on the battle to come. That was what mattered. Anything else could be dealt with later if/when they survived the impending fight with a maniac commanding a demon army.

Alec was lurking awkwardly where she had left him. Disdainfully ignoring the dithering Inquisitor, she frowned at her brother. "Go get ready," she ordered briskly "We're sailing for Valentine's ship right away." The corner of his mouth twitched upward, though Angel knew what there was to smile about. She could only presume he was as eager to inflict grievous bodily harm on Valentine Morgenstern as she was.

"Is that for me?" He asked, indicating the naginata she had picked up for Maryse – it was her mother's weapon of choice.

"Get your own!" She jerked it out of his reach and he turned, looking fondly exasperated, presumably to head to the Weapons' Room.

Instead she handed the blade to its intended recipient, who, to her surprise, pressed a fierce fleeting kiss to her forehead before spinning the naginata expertly in her grasp.

"Thank you, Isabelle," Maryse said, and with one swift, fluid movement, lowered the blade so that it pointed directly at the Inquisitor's heart.

Imogen Herondale looked up at Maryse with the blank, shattered eyes of a ruined statue. "Are you going to kill me Maryse?"

Maryse hissed through her teeth "Not even close," she said. "We need every Shadowhunter in the city, and right now, that includes you. Get up, Imogen, and get yourself ready for battle. From now on, the orders around here are going to come from me." Izzy swelled with satisfaction and awe watching her mother put the infuriating Inquisitor in her place. She loved when her mother was, admittedly restrainedly, affectionate and intimate with her, but she also loved watching her mother being a terrifying professional as she was now. She looked magnificent – like a true Shadowhunter warrior, every line of her blazing with righteous fury. Maryse continued "And the first thing you're going to do is free my son from that accursed Malachi Configuration." Another little swell of love burst in Izzy's chest, flooding her with warmth as she heard Maryse refer to Jace as 'my son' without even thinking about it, as if it were the most natural thing in the world.

The moment was tarnished slightly by the realisation that she and Alec were now going to have to explain the conspicuous lack of said son. Exchanging a glance with her, her older brother cleared his throat and began "Actually, there's something you should probably know…"