After pocketing the mysterious diary in Moaning Myrtle's bathroom, Cassandra backtracked across the castle. She headed to her thinking spot at the top of the Astronomy tower, where she was guaranteed some privacy.

She sat on the stone floor and set the book carefully in front of her. It was soaked in water. She took her gloves off, pulled out her wand and gave it a complicated little wave so that hot air streamed out of the tip; she then pointed this at the diary, which began to steam as it dried out.

"That's better," she muttered to herself.

She used another charm to peel the now dry pages apart. They were thick vellum and completely blank. On the back cover of the book she saw the printed name of a variety store in Vauxhall Road, London.

Riddle was not a wizarding surname, which meant the owner of the diary had been a half-blood, at best. That he had dawdled around Vauxhall before it'd been largely destroyed during the Second Muggle War told her he'd been poor as well.

The next step in uncovering the diary's secrets was to cast every single revealing spell she knew. A few were included in the Hogwarts curriculum, most had been taught to her by her grandfather or by Boris Ivanovich, a retired Durmstrang Dark Arts Professor and her private tutor over the summers.

If either of those men could see her messing about with a cursed object unsupervised, they'd hex her hair off her scalp. But her grandfather was dead and Ivanovich was holed up in Siberia and there was something about the book that awoke a curiosity inside of her she didn't want to ignore. Maybe it was a bad idea, but she would indulge anything that had the capacity of taking her out of the stupor she'd been drowning in as of late.

She tried the revealing spells one by one, in alphabetical order:

Aparecium

Appare Vestigium

Misterya Fateor

Reserare Maledictum

Revelet Absconsa

Revelio

Specialis Revelio

Verbis Aperio

Nothing happened. She took a breath, exhaled, closed her eyes, focused on her intention — finding out the truth of the diary — and tried again, this time by magnitude of spell strength.

Still nothing.

Klaus croaked from his perch above her.

"I agree, it is odd," Cassandra said.

She tilted her head sideways, slowly rotating it in a full circle to loosen her neck muscles. She hadn't performed particularly challenging magic in weeks, had spent the majority of the past month asleep, and as a result felt uncharacteristically tired from casting the spells.

"Lazy," Cygnus Black tutted in the darkness of mind. "Lazy and weak."

Cassandra researched incessantly for two weeks before reporting back on her discoveries to Fred and George Weasley. The three of them were sitting at the very back of the Charms class with a table to themselves. They were supposed to be practicing the opposite of the Summoning Charm today — the Banishing Charm. Owing to the potential for nasty accidents when objects kept flying across the room, Professor Flitwick had given each student a stack of cushions on which to practice, the theory being that these wouldn't hurt anyone if they went off target. It was a good theory, but it wasn't working very well. Slytherin and Gryffindor students, always at odds, kept sending much heavier things flying across the room — Professor Flitwick, for instance — trying to hit one another.

"You really think it's cursed?" said Fred, reaching for the diary.

Cassandra hit his hand with a stinging hex.

"Ouch!"

"Don't touch it," Cassandra said crossly. "And yes. It's been constantly calling to me, wanting to be written in. It probably called to your sister in the same way. Only cursed objects are able to perform compulsions."

"Did you write in it?" Fred asked as Professor Flitwick went whizzing resignedly past them, landing on top of a large cabinet.

This class was an ideal cover for a private conversation, as everyone was having far too much fun to pay them any attention. Cassandra had been recounting her discovery and investigation of the little black book in whispered installments for the last half hour.

"Of course not, I'm not a moron," Cassandra whispered.

Fred flicked her forehead lightly. "That's our little sister you're talking about."

Cassandra rolled her eyes. "She's eleven. She's supposed to be a moron."

"D'you know who he is? T. M. Riddle?" said George, his eyes alight with interest as he Banished a cushion with a sweep of his wand (it soared into the air and knocked Kenneth Towler's hat off).

Cassandra looked at the Weasley twins sympathetically. "From what I've managed to gather so far, Tom Marvolo Riddle was a Slytherin. He attended Hogwarts from 1938 to 1945. He was a prefect and head boy and — here is where it gets bad for Ginny, he received an award for special services to the school in 1943."

"Why would that be bad for Ginny? Riddle was Percy's wet dream, so what?" said Fred, waving his wand without paying much attention, so that his cushion did an odd sort of belly flop off the desk.

"Fred, 1943 was the last time the Chamber of Secrets was rumored to have been opened. A student was killed and Hogwarts was due to be closed before someone allegedly caught the culprit."

"Riddle caught the Heir of Slytherin?"

"Riddle caught Rubeus Hagrid."

"What?" said Fred and George, their eyes widening, their cushions spinning high in the air, ricocheting off each other, and dropping heavily onto the floor.

Cassandra leaned in. "I combed through every single edition of that year's Daily Prophet, as well as publicly available school records. Rubeus Hagrid was the only student expelled from Hogwarts in 1943, no reason listed. Tom Riddle was awarded not long after."

"I don't understand," said George. "You can't think Hagrid's behind the attacks. He's got a soft spot for large monstrous creatures, but he's a good bloke!"

"And what in Merlin's saggy bollocks does our sister have to do with any of this?" said Fred indignantly.

Cassandra shook her head sceptically. "I don't think Hagrid was the one who opened the Chamber of Secrets, either time. He doesn't fit the profile for the Heir of Slytherin at all. I think Tom Riddle did it. I think that Riddle opened the Chamber of Secrets back in '43, that he framed Hagrid for it, and that he left his cursed diary behind to compel someone into continuing his work. And I think he was using Ginny to open it this time around."

She Banished a cushion and it flew across the room and landed in the box they were all supposed to be aiming. The twins were looking at her, their faces ashen.

"This is a load of dung." Fred angry-whispered. "George, tell her she's off her rocker. This is Ginevra we're talking about. She dots her i's with little hearts and thinks she's going to marry Harry Potter one day. She's not going around petrifying people and writing creepy messages on the castle walls with blood. Ginny would never do that."

Cassandra went on. "I'm talking about compulsion, Fred. Maybe even possession. It doesn't matter what your sister would or wouldn't do, because she wasn't the one doing it. Ginny might've been riding the broom, but she wasn't the one steering it."

"You're making leaps you don't explain," said George, but he was thinking about what she'd said.

"The facts explain," Cassandra shrugged.

"You need to get more facts, then. We need… Look, it's not that we don't believe you, alright?" Fred said more calmly. "But you haven't even written in the diary. How can you be sure it's all that evil?"

"Fred," George said. "What does dad always say? Never trust anything that can think for itself…"

"...if you can't see where it keeps its brain. I know, George. But we don't even know that this diary can really think for itself. All she's said is that the thing wants to be written in. She could be imagining it. No offense, Cassandra, but you haven't been a shining picture of mental stability lately."

Cassandra felt a rapid flash of irritation. "You try fighting a pack of werewolves hell-bent on eating you and we'll see how well-adjusted you come out."

"Cass, he didn't mean —"

"Whatever, George. Hand me a quill, will you?"

"What?"

"Just give me a bloody quill, or am I going to have to conjure one?" she snapped.

The boys quickly rummaged through their pockets while Cassandra discreetly pulled on her dragonhide gloves.

Fred sheepishly offered her a dingy-looking goose quill. "Here. It's self-inking. I really didn't mean —"

Cassandra raised a gloved hand, stopping him. She opened the diary and flicked through the blank pages. She felt the now-familiar feeling she associated with the little book, a sharp pull deep in her chest that told her she was meant to be holding it.

The three teenagers hunched over the desk, staring at the book intently.

"Hello," Cassandra wrote in elegant cursive script onto the first page.

The ink shone brightly on the parchment for a second and then, as though it was being sucked into the page, vanished. Then, oozing back out of the page, in the same ink, came words Cassandra had never written.

"Hello. My name is Tom Riddle. Who are you?"

The Weasley twins gasped and Cassandra slammed the book shut, shoving it in her bag.

"Is that proof enough for you?"

"We need to take this to McGonagall now," said Fred.

George shook his head. "Fred, we can't."

"Why not?"

"They expelled Hagrid, and he didn't even have anything to do with the attacks. What do you think they'll do to Ginny?"

"We'll tell them it wasn't Ginny's fault. Cassandra can explain what happened. Dumbledore will understand."

"It's not Dumbledore you need to worry about. Lucius Malfoy is on the Board of Governors," said Cassandra, taking her gloves off and putting them in her bag, to cover the diary. She'd heard about Lucius and Arthur Weasley coming to blows at Flourish and Blotts months back.

George turned to her. He ran his hand over his forehead and took a deep breath. "We're screwed. Lucius Malfoy's been after dad all year because of the Muggle Protection Act dad's trying to pass with the Ministry. He's going to use this to destroy dad's career."

Cassandra didn't say anything, sending another cushion zooming neatly into the box. It was the truth.

"What do we do, then? We can't do nothing," said Fred, sending a cushion soaring into the window.

"I could try to get information from the diary," said Cassandra. "If I pretend to go along with Riddle's plans, maybe I can get him to tell me where the Chamber is, how to open it, what sort of creature lives in it. You could use that information as leverage to protect your family."

"That's brilliant," Fred said with a grin, but he caught Cassandra's eye and looked at the ground without another word.

"But what if it tries to possess you?" said George.

"I'm a more than competent Occlumens. That doesn't guarantee I'll be able to resist the diary's enchantments, but it gives me much better odds than your sister ever had."

Fred and George looked at each other, communicating silently. They were as subdued as she had ever seen them. She supposed she would be too, in their place.

"Should we talk to Ginny about this?" asked Fred, sounding as if he'd asked the question entirely against his will. "Maybe she knows something that can help.''

"I can't answer that. It's not my choice to make," Cassandra said. She hadn't been shielded from much throughout her life, but she would understand if the older Weasleys chose to spare their little sister from being confronted on her recent unintentional violent actions. "And there is always the chance she doesn't remember much at all from the incidents."

"You think so?" said George. He looked very hopeful that she would say yes, so she did.

Respectful of the twins' wish of uncovering the mysteries of the Chamber of Secrets without involving their sister, Cassandra turned her attention in earnest to the most urgent problem facing her: how to convince the diary to spill its secrets to her. That night, she reinforced the Imperturbable Charm around her bed, cycled through her usual Occlumency exercises, careful to reinforce the fortress around her mind, and for a second time, put a quill to Tom Riddle's journal.

Excited and apprehensive, she wrote, "Hello, Tom. My name is Bellatrix Lestrange."

Cassandra might be an idiot for doing this, but she wasn't enough of one to give a powerful cursed object her real name.

She watched, expectant, as the words lingered and set on the page, then disappeared without trace, before a response appeared in slightly uneven, spider-thin script.

"Hello, Bellatrix. It's a pleasure to meet you. How did you come by my diary?"

These words, too, faded away, but not before she had started to scribble back.

"I took it."

"By force?"

Cassandra hesitated, her quill suspended over the diary. It wouldn't do well to inform the Dark object that its last owner had tried to flush it down a toilet. She liked most of the Weasleys she knew.

"Are you angry?"

"Why would I be angry? You must be an extraordinarily powerful witch, Bellatrix. I am very lucky to be in your hands. I am only curious as to why you decided to take me from the last person who had me in their possession."

"I felt your magic calling to me. I can sense how strong you are, Tom. The witch who had you didn't deserve something this powerful. You might not know this, but her family are a bunch of Mudwallowers. Not worth the second-hand wands they yield."

She waited eagerly for Riddle's reply. Pureblood supremacists tended to be suckers for flattery, no matter how empty it was.

"That's very impressive, Bellatrix. Not many witches would be capable of sensing the magic this diary holds. But then again, Lestranges are no ordinary wizards."

"How do you know my family?"

"I wrote this diary when I was a student at Hogwarts School of Witchcraft and Wizardry. Lautaro Lestrange was a close confidant of mine. I presume you are one of his descendants."

"He was my grandfather."

"Then our meeting was fated, dear Bellatrix."

"What do you mean?"

Riddle's reply came quickly, his writing becoming untidier, as though he was eager to tell his story.

"I made this diary to record my memories in some more lasting way than ink, because I always knew that there would be those who would not want it read. Those who are opposed to the triumph of Wizardkind over Muggles. Who in their foolishness do not recognize our right to rule this world and ensure our prosperity. This diary holds memories of amazing things, Bellatrix. Things that were covered up. Things that happened when I, the Heir of Slytherin, opened the Chamber of Secrets."

Cassandra startled so hard at the words she nearly upset her ink bottle. It was unnerving and satisfying, in equal measures, to have her theory confirmed.

"In my day, they told us it was a legend, that it did not exist. But I knew it was a lie. In my fifth year, I found the Chamber and set the monster free. It attacked several Mudbloods, finally killing one. But they intended on closing Hogwarts because of it, ashamed of what had happened, indifferent to Salazar Slytherin's legacy. So I framed someone else for it, someone who didn't deserve to be at Hogwarts in the first place and he was expelled. A story was given out that the girl had died in a freak accident. They gave me a nice, shiny, engraved trophy for my trouble and warned me to keep my mouth shut. But I knew it could happen again. The monster lived on, and the one who had the power to release it was not imprisoned."

"You."

"Yes, me. And now, you."

Cassandra's heart was hammering.

"I can show you, if you like," wrote Riddle. "You don't have to take my word for it. I can take you inside my memory of the night when I first opened it."

What did Riddle mean? Should she say yes? Would accepting his offer open her mind to his invasion? She glanced nervously at the door to the dormitory, which was growing dark. When she looked back at the diary, she saw fresh words forming.

"Let me show you."

Cassandra paused for a fraction of a second then wrote three letters.

"Yes."

The pages of the diary began to blow as though caught in a high wind, stopping halfway through the month of November. Cassandra saw that the little square for November nineteenth seemed to have turned into a minuscule painting. Her hands trembling slightly, she raised the book to press her eye against the little window, and before she knew what was happening, she was tilting forward; the window was widening, she felt her body leave her bed, and she was pitched headfirst through the opening in the page, into a whirl of color and shadow. She felt her feet hit solid ground, and stood, shaking, as the blurred shapes around her came suddenly into focus.

She immediately came face-to-face with a terribly handsome boy of about sixteen. A silver prefect's badge was glinting on his chest. He was much taller than Cassandra, but he, too, had pale skin, jet-black hair and the fine aristocratic features shared by many pureblood families.

"Tom?" she said tentatively. But the wizard didn't react. He kept staring past her — through her — as if she weren't there at all.

"Like watching a memory in a Pensieve," she murmured.

She turned around, looked at her surroundings, and realized she had no idea where in the castle they were. It was some sort of tunnel, wet and dark and large enough to stand in. She squinted around at the slimy stone of the dark walls. "Maybe under the lake…"

Just as she'd taken her wand out to perform a Wand-Lighting Charm, Riddle flung a bright orb of light away from his fingers into the darkness, in an extremely impressive display of wandless, wordless magic. Satisfied, he silently slinked past Cassandra further into the channel. She followed him.

The tunnel was quiet as the grave, the only sound coming from the soft slap of Riddle's footsteps on the wet floor. Even with the orb of light floating in the air, it was so dark that Cassandra could only see a short distance ahead, and Riddle's shadow on the walls looked monstrous in the magical light. She didn't have a shadow at all.

Riddle continued to lead the way forward, turn after turn and bend after bend. Every hair on Cassandra's body was standing up. She wanted the tunnel to end, to know what she'd see when it did. And then, at last, as they crept around yet another bend, she saw a solid wall ahead on which two entwined serpents were carved, their eyes set with great, glinting emeralds.

Riddle approached it, his body drawn taut as a bowstring. He touched the strangely alive-looking stone snakes with reverence.

The wizard cleared his throat, and the emerald eyes seemed to flicker.

He said something in a low, faint hiss. Parseltongue, she thought to herself. He is the Heir. The serpents parted as the wall cracked open, the halves slid smoothly out of sight, and Cassandra, her hand impossibly tight around her wand, walked inside after him.

They crossed the entrance to a very long, dimly lit chamber. Towering stone pillars entwined with more carved serpents rose to support a ceiling lost in darkness, casting long, black shadows through the odd, greenish gloom that filled the place.

She watched Riddle pull out his wand and move forward between the serpentine columns, gliding behind him. Every careful footstep of his echoed loudly off the shadowy walls. He kept his eyes wide, as if trying to drink in every possible detail.

When they drew level with the last pair of pillars, a statue high as the Chamber itself loomed into view, standing against the back wall.

Cassandra craned her neck to look up into the giant face above: It was ancient and stern, with a long, thin beard that fell almost to the bottom of the wizard's sweeping stone robes, where two enormous gray feet stood on the smooth Chamber floor. Any Slytherin student could have recognized it.

"Finally," said Riddle, his voice thick with some unidentifiable emotion.

And then he laughed, a high, cold laugh that didn't suit his handsome, boyish face. It jostled something deep in Cassandra's subconscious.

Still standing between the high pillars and looking up into the stone face of Slytherin, high above him in the half-darkness, Riddle opened his mouth wide and hissed once again — but this time, even though she shouldn't, Cassandra understood what he was saying…

"Speak to me, Slytherin, greatest of the Hogwarts Four."

Slytherin's gigantic stone face started moving. Awestruck, Cassandra saw his mouth opening, wider and wider, to make a huge black hole. And something was stirring inside the statue's mouth. Something was rising up from its depths.

Something huge hit the stone floor of the Chamber. Cassandra felt it shudder — she knew what was happening, she could sense it, could almost see the giant animal revealing itself from Slytherin's mouth.

And then, as Cassandra reached forward to see it, she jolted awake in her bed, soaking wet with perspiration, holding the diary tightly to her chest.