The usual disclaimer:

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Still wearing his Invisibility Cloak, Harry dashed madly through the halls of the building. He tried to use the Marauder's Map to find who he was looking for, but couldn't even read it because of the tears that clouded his vision. Finally, he went into the Great Hall and just sat in the middle of the floor.
After sobbing loudly for a few minutes, and pounding his fists on the ground like a child having a tantrum, he managed to see through his frustration. He still couldn't read the tiny words on the map properly, so he decided that if he couldn't find Snape, he would just make Snape come to him.
Harry touched his wand to his forehead and drew on his all his anger and bitterness. The negativity was easy to transform into a burning pain, which he willed to affect not only himself but Snape as well. A few minutes of this produced the desired results, and one of the dots on the Marauder's Map left its room and began moving through the halls.
Being still invisible, Harry found his old teacher before being sighted himself. "Professor...Hey..."
Snape looked around, confused, until Harry took off the cloak. He sighed with irritation. "I had a feeling it was you..." he paused and looked at Harry's face. "What on earth...?"
Harry responded in a hysterical voice that greatly contrasted Snape's careful whisper. "Something terrible happened, Snape I'm going to be sick, really it was awful, I can't believe I-"
In an instant they were both surrounded by a pearly-white bubble. "Before you go spilling your secrets to the entire school, Potter, you might want to think about a silencing charm first," Snape lectured calmly. He sounded tense but collected as he demanded, "Now, tell me what happened."
Harry drew in a deep breath and, periodically pausing to breathe and wipe his eyes, recounted the night's events. Instead of looking away tactfully to allow Harry to hide his crying, Snape watched him sob the whole time, with a contemptuously critical air.
Eventually Harry just gave up pretending that he wasn't distraught, and sniveled, "I'm so upset - this really messed me up..."
"Why? Nothing happened."
"It wasn't nothing! It's not, Snape, it was awful, I watched them-"
"So?" he demanded scornfully. "You watched them torture an innocent for a few minutes. So what? That's nothing, believe me, nothing compared to what could have happened. I told you from the start that you're a child, unprepared for all of this...You're just lucky that they didn't make you curse the girl yourself, or kill her for that matter. You're complaining about nothing, Potter."
Harry started to sob out an answer, but he was interrupted. "Do you expect me to feel sorry for you? I've already told you what I had to do to combat the Dark Order. What you did tonight was nothing. Stop this ridiculous whining at once."
Finally Harry got a word in edgewise. "But it was my wife," he whimpered miserably. "I love her."
"And she's alive and you should just be thankful for that." He waited until Harry had regrouped himself slightly. "What is of more concern to me, though, is that you seem to be losing your hold over the Dark Circle. And that our plans are ruined because you have so stupidly agreed to a massacre that we have only two days to prevent. Let's go to my office, right now, and figure out what to do."
Snape swept away coldly, and casually sent a counter-charm over his shoulder to make the silencing bubble disappear. Harry had no choice but to follow him, still trying to fight back tears.

Snape sat down at his desk and conjured up a bottle of brandy. "Much as I hate to do anything which might begin to produce an atmosphere of camaraderie, I suppose I'll have to offer you a drink. Sit."
Harry sat. He knew he looked a mess. "Thanks - I feel terrible."
The scowl grew sourer. "Try not to sound like you're talking to a friend. I would like, if it's at all possible, to preserve what animosity remains between us."
Laughing suddenly, Harry answered, "My pleasure, you cranky old nut."
"That's better." He poured out two drinks and heaved a sigh. "All right, now tell me again what happened today. Particularly between you and Malfoy - that sounded rather alarming to me."
Harry explained it all and Snape nodded knowingly. "I suspected as much. Potter, you can't promise them world domination and then refuse to let them kill like they want to. They won't obey. I suppose, after all, it was a good move to set a date for the attack on the Ministry...it was probably the only thing you could possibly have done to prevent a mutiny."
Harry began to outline an idea that had occurred to him the other day. Would it be enough, he wondered, to have confessions recorded? Or did they need to be actually seen first-hand by live witnesses?
He described the term "video camera" to Snape, who listened skeptically. "I believe I've heard of that apparatus... It records memories so that anyone can see them later, correct?"
"Yes. So if we get somebody to tape them making evil plans and confessing to evil stuff they've already done..."
After about a half hour of ironing out the details, the plan made perfect sense... except for one thing: Snape thought it safest if no one else was involved, but he didn't know how to work a video camera himself. And since they had to catch the Circle on tape the following evening, there would be no time for Harry to go get one to teach him with.
He was trying to explain it now, without actually having a camera in front of him, but they weren't making any progress. All of a sudden, a cackle sounded in the corridor.
It was Peeves. "CAUGHT YOU!" he screamed at someone, presumably a student. Snape jumped up and hissed to Harry, "Cover yourself!" and opened the door of his office.
Harry scrambled under his Invisibility Cloak and tried to listen to what was happening as the professor took charge of the situation. "Wandering about after hours, are we?" Snape's voice had a strange sort of triumph to it. "Thank you, Peeves," he said silkily, "but I'll take it from here."
Harry heard Peeves bang away down the hallway. Snape's voice was cold and commanding now. "Back to your dormitory, Miss Simmons. And you - what are you doing out this late? Both of you, come into my office at once."
A petulant girl's voice rang out, "But, sir, what about them? Are they going back to their rooms now too, or are they in trouble? It was my fault just as much-"
"Go!" Snape ordered angrily. "What happens to them is not your affair. You're just fortunate not to be in as much trouble as they are."
Harry heard the girl scamper off, and the door to Snape's office opened again. "In here, you two," he said softly. When the two students entered the room, Harry could barely restrain himself from ripping off his cloak to say hello.
It was Sophie and Julien.

Julien looked terrified and hopeless. Sophie's face, on the other hand, wore a look that Harry recognized. He knew what thoughts that must be passing through her head... "Oh, we're caught. Quick, think! What can I tell him? Oh, no, we're in trouble. How can I get out of it?" Thoughts that had been so familiar to him back in the day...
Sophie, though, had options that Harry had never had. Snape made no move to stop her as she cleared her throat and began to explain herself, "Professor...er...It's my fault. I was just taking Gina Simmons to meet my brother... I think she likes him... They don't have a single minute of their schedules together - this is the only time we had - I know we're out late... It's my fault though... Am I in a lot of trouble?"
Snape let her finish, but then glowered at her. "Miss Potter, I will no longer allow you to take the blame for your brother's misbehavior. This time, it will be my pleasure to give him the most awful detention I can possibly conjure up. However, as to being in trouble, you happen to be just the opposite." He turned and looked directly to where Harry was sitting, invisible. "You see, I think you can actually help me avoid a great deal of trouble. Do either of you know how to use a video camera?"
That question made Harry jump out of his seat. Without even bothering to become visible, he exclaimed, "No, Snape, I won't involve them! Stop it."
"Dad?" Julien asked incredulously, looking around. When Harry took off the cloak, he and Sophie both ran forward to greet him. "What are you doing here?"
Snape answered Harry's comment. "How else do you intend for me to get the thing on film? We have only one chance and it is imperative that we not make mistakes."
"Are you nuts? It's too dangerous!" yelled Harry.
"Dangerous?" hissed Snape, beginning to sound quite insane. Oh, no, Harry thought. He vividly remembered what a frightening sight Professor Snape was when he'd worked himself up like this... Harry and his children stared as Snape shook his head and repeated himself even more vehemently. "Dangerous? No, let me tell you what is dangerous. What is dangerous is not capturing the evidence we need tomorrow night. What is dangerous is choosing a conspirator whom we cannot trust. You have already done the things that are dangerous, Potter. Now, I assume your children are not Dark Circle sympathizers themselves? No? Then they are the best allies we could possibly find. I can't believe I didn't think of this earlier."
By now, Sophie and Julien had gotten the gist of what was going on. "You're working against the Dark Circle, Dad?," Julien asked excitedly. "You have some plan to break it up?"
"We'll help!" Sophie said. "We want to. We don't care if it's dangerous, Dad, we want to help!"
"And so you shall," Snape said. "Now sit down, and don't interrupt, and listen carefully to what you have to do...."
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It was almost dawn by the time Harry got back home. He'd been plotting with Snape until well past three o'clock, then had wandered around aimlessly, trying to postpone the moment when he would walk in the door and see Gabrielle. He still thought he'd have trouble talking to her without breaking down.
When he did finally tiptoe into his darkened bedroom and lie down, though, he suddenly wished that maybe he had come home a little sooner.
Because Gabrielle was gone.

"Lumos!" Harry shined light around the entire bedroom. Gabrielle was not in the bed, or on the chair, or by her dresser. He jumped up and checked the rest of the house, calling her name, but she wasn't there either.
He could feel his heart pounding as he tried logically to figure out what might have happened. Just when he was about to panic, fearing that she'd been kidnapped by overzealous Dark Circle members, he saw a note on her pillow.
Please don't come after me, it said in Gabrielle's beautiful handwriting. I beg you. I won't tell a soul, I swear it. I'll keep your secret. I'll do anything, only don't hurt the children. Please. Forget about me, I'll never bother you again. - Gabrielle
Is the note for me? Harry wondered. It can't be. Hurt the children? Why on earth would I hurt the children? Gabrielle's note sounded truly terrified. This didn't make any sense...Unless she was talking about his secret life...but it couldn't be. He'd Apparated to the place where he met the Circle, so there was no way she could have followed him and seen him transform. She couldn't know. This made no sense at all.
He walked through the house, looking for more clues about where she had gone and why, but found nothing until he came to the kitchen.
There, cauldrons were tossed all over the floor as though a hurricane had come through. The cabinets had all been ransacked as though someone were trying to rapidly cook an extremely difficult dish...
... or brew an extremely difficult potion.

One cauldron sat out in the middle of the floor, still bubbling with some mixture. Next to it, a partially incinerated piece of paper caught Harry's eye. It was a bill from an emergency potions delivery service. Most of the order was burned away, but "lacewing" and "boomslang" were still visible.
Harry bent down to smell the mixture. He recognized the odor - it was Polyjuice Potion.
So Gabrielle is disguising herself? he wondered. He had no idea why she wanted to run from him all of a sudden, or why she had left the remains of the potion on the floor. After all, if he really wanted to find her, all he would have to do would be to drink some himself. That way, he'd know what she looked like and it wouldn't be so hard to track her down.
And he definitely wanted to track her down. Where on earth had she gone?
Without further ado, Harry gulped some of the potion and waited for it to take effect. Soon, the painful ripping sensation occurred, that told him that he was transforming. He sat on the floor groaning for a few minutes, then rose and dragged himself to a mirror.
He looked in and stared with utter disbelief on his face.
Harry looked exactly the same. He had turned into... himself....?
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Sorry this is a bit of a cliffhanger, everybody! I usually hate doing that to people. But this chapter was too short if it stopped before Harry got home, and too long if I added the next bit. So you'll just have to wait a day or two before finding out why Gabrielle made a Polyjuice Potion of Harry...if indeed it was Gabrielle who did it. It's a good reason. Can anybody guess?