Author's Note: So, this fic came out of a challenge to write for a completely random pairing. The paring I ended up writing was Marius Black/Olive Hornby. I worked out that they could well have been the same age and so this story was born. Hope you enjoy it!

Cassiopeia Black was sitting cross-legged on the floor of her bedroom, laughing with her best friend. It was a week before the two Slytherins were due to return to Hogwarts for their fifth year and a visit to Diagon Alley was extremely necessary. Cassiopeia, as an underage, unmarried witch, was not permitted to visit London without a chaperone and so she and her best friend had been forced to wait until her father, Cygnus, was finished with his Ministry guests.

"You know what I think is outrageous, Olive?" Cassiopeia asked, halfway through scribbling a letter to her elder sister, Dorea.

"What's that?"

"Mudbloods," Cassiopeia shuddered and wrinkled up her nose in distaste. "How can they possibly have as much magical skill as we do?"

"I don't suppose they do," Olive replied, flicking through Transfiguration Today, with a bored expression upon her face.

"Take that Myrtle in our year," Cassiopeia continued. "She's in Ravenclaw! How can a Mudblood be in Ravenclaw? I was under the impression that they were supposed to be intelligent!"

"I don't think Myrtle is particularly stupid," Olive shrugged. "She's just a bit weird. Spends all her time either moping or studying." Cassiopeia frowned.

"Don't shrug like that, Olive," she reprimanded her friend. "It's not ladylike. And you oughtn't defend Mudbloods. Myrtle was probably their statistical Mudblood." Cassiopeia added nastily. "They have to let at least one in with each Sorting, don't they?"

"I'm not sure it works that way, Cassie," Olive began but her friend wasn't listening.

"You know, sometimes I think you should have been in Gryffindor," Cassiopeia complained. "You spend too much time sticking up for everyone. You know her blood isn't as pure as mine, so why bother wasting time with her?" Olive sighed quietly but didn't reply.

"Did I tell you the news anyway?" Cassiopeia looked up, after writing a few more sentences of her letter. "Dorea's marrying Charlus." Olive hardly looked up from her magazine.

"Charlus?"

"Honestly, Olive, don't you know any esteemed wizarding families? It's Charlus Potter."

"Potter?" Olive glanced up. "Isn't he a bit…?"

"A bit what?" Cassiopeia frowned.

"A bit Gryffindor," Olive finished. "He's hardly a Flint, or a Lestrange, is he?" Cassiopeia's frown deepened.

"He's a pureblood," she replied, as if that settled the matter. "That's all that's important, really."

Outside the bedroom door, Cassiopeia's brother, Marius, was listening to his little sister's conversation. Despite being two years older, he did not attend Hogwarts School of Witchcraft and Wizardry alongside her because as much as the Black family hated to admit it, their eldest son was a Squib and unable to perform even the most basic spells. Unlike many other Squib children, Marius was not permitted to attend a Muggle school. The Black family kept him at home, out of fear and shame and very few people even realised that Cygnus and Violetta had two sons. Pollux, their youngest child was just starting his second year at Hogwarts and had, in his parents' eyes, more than made up for his elder brother's lack of magical skill. He was one of the brightest wizards in his year and the Black family had high hopes for him.

The bedroom door swung open abruptly. Marius quickly stepped back but Olive stopped in her tracks and watched him curiously.

"Who are you?" she asked, suspiciously. Marius swallowed and remembered the lie that his parents had taught him for unavoidable occasions such as these.

"I'm Marius," he replied, holding out his hand. "I'm a distant cousin of Cassiopeia's. I…came to congratulate Dorea on her engagement."

"Hello," Olive smiled pleasantly. "I'm Olive Hornby, a friend of Cassie's from school."

"It's very nice to meet you." Marius knew that he would likely be punished later for introducing himself but he resented being shut away forever. After all, it wasn't his fault that he'd been born without any magical ability.

"So, are you at Hogwarts too?" Olive frowned. "I don't recall seeing you around."

"Oh no, I'm…"

"Have you left?" Olive continued. "Cassiopeia hasn't mentioned you. Does she know you're here?"

"Um…" Marius shifted his weight to his left foot awkwardly. "Yes, she knows."

"Alright," Olive smiled slightly, looking sympathetic. "How long are you here-"

Olive never got to finish her question because at that moment, Cassiopeia burst out of her room, scowling at her brother, her eyes flashing with anger.

"What are you doing, listening at my door?" she snapped. "Go upstairs. When father hears about this, he won't be happy." Marius gave Olive an apologetic glance whilst she stared at her best friend in shock, wondering what in Merlin's name Marius had done to annoy her.

"Sorry," Marius told Olive and turned away to head towards the staircase leading to his attic room.

As soon as he'd disappeared, Olive turned to her friend.

"What was that all about?" she asked, slight irritation in her voice. "We were only having a conversation."

"Not here," Cassiopeia muttered, pulling Olive back into her bedroom and closing the door behind them. "Merlin, this is so embarrassing. I can't believe that I'm actually going to have to tell you this."

"What is it?" Olive probed, racking her brains for an explanation. Cassiopeia sat down and indicated for Olive to do the same.

"He's not my cousin, he's my brother." Cassiopeia spoke very quickly and without looking at her best friend. Olive's mouth fell open.

"He's your what?"

"My brother," Cassiopeia muttered. "And don't gape like that, it's not very becoming." Olive's mind was reeling.

"How… you only have one brother… don't you?"

"Yes, well, no one knows about Marius," Cassiopeia replied, spitting out her brother's name as if it were poisonous. "He's… Merlin, you have to swear not to tell anybody about this…"

"I promise," Olive nodded. "Go on."

"He's a Squib," Cassiopeia whispered, closing her eyes as if in agony. "It's awful, isn't it?" Olive couldn't stop the loud gasp that escaped her and she quickly clapped her hand over her mouth.

"Cassie, really?"

"It's so embarrassing," the other girl continued, grimacing. "We're supposed to be such a noble family and then we've got someone like him living with us." Olive blushed.

"Well, he didn't seem too awful," she shrugged. "He's polite enough."

"Olive!" Cassiopeia snapped. "How many times do I have to tell you, don't shrug like that!" She took a deep breath. "It's not a matter of his being polite. He can't do magic. He can't do magic at all. That's just about the worst thing I can imagine."

"Well," Olive whispered, not wishing to agree with her friend. "What happens with him?"

"He has to stay here," Cassiopeia frowned. "Until he's of age. When he's seventeen, we'll formally disown him and he can start making his own way. Until then, he has to stay. It's too difficult to force him to leave until he's legally an adult because the Ministry have to be involved and father doesn't want everyone to know that he and mother produced a son like… like that." Cassiopeia looked tearful and Olive couldn't quite believe what she'd heard.

"Doesn't he leave the house?" she asked. Cassiopeia stared at her, horrified.

"Of course not!" she exclaimed. "He'd humiliate the entire family! Our esteemed name would never be so revered again!"

Olive didn't think she'd ever been so shocked in her entire life. She'd met Marius, who she'd presumed to be a respected member of the Black family, only to discover that he was in fact a Squib and incapable of doing magic. How her best friend had kept the secret from her for so many years was beyond Olive.

"You know what infuriates me more than anything?" Cassiopeia sniffed. "There are girls like that Myrtle at Hogwarts, who come from Mudblood families. They don't need magic. She would have lived a perfectly happy life without ever being a witch. It's not fair that families like ours should have to endure such humiliation when she's taking up a place at Hogwarts. That should have been my brother's place. He should be learning magic. He'd be in seventh year, this year." Olive noted that her friend was talking about Marius as if he'd died. She felt a strange rush of dislike towards Myrtle, the Muggle girl who didn't realise how much pureblood families suffered with non-magical relatives amongst them.

"It's not fair," she whispered. "You're right." Olive didn't know whether to feel scared at the sudden resentment that she felt for all Muggle-born witches and wizards. Perhaps it would be easier and less painful if magic was reserved for pureblood families only. Girls like Myrtle wouldn't suffer, she told herself. Myrtle would have been perfectly content to live life as a non-magical woman. Marius however, was shunned, his family were ashamed and he was forced to hide and lie because he didn't have any magical ability.

How in the world, Olive wondered to herself, as she stared at her best friend's miserable face, was that fair?

Olive resolved to be much less tolerant of Myrtle when they returned to school in the summer. It wasn't right for her to stick up for the swotty teenager, not when Olive had seen what trouble her best friend faced. Tom, a handsome prefect in her year definitely had the right idea; witches and wizards needed to defend the purity of their bloodlines or pay the price. Obviously, Olive realised, somewhere centuries ago, the Black family must have failed to keep their bloodline pure. That was the root of the problem which resulted in Marius.

Ultimately, it was easier to blame Mudbloods like Myrtle for Marius's problems than his own ancestors. Girls like her would only contribute to the decline of the pureblood families.