[The Categories Challenge: Prompt - Trapezium Song - Trap Door, OneRepublic Category - Style]

[The Gemstone Competition: Aquamarine - write about a strong friendship.]

[Star Light, Star Bright Challenge: Star - write about a character who is now deceased.]

You say you're a minute from the deep end,
You cut cold the courtesy, it's sink or swim now,
and your body's aching for a breath - I'll give it to you
With a trap door to take care of all of this.

- Trap Door, OneRepublic

Even later, when it was all over and the bodies were safely underground, nobody could really put a finger on why those four particular boys had gotten along so well.

They were so different, after all, from their families to their personalities to the ways they eventually died. They were from different worlds, and they were on different paths, and the only reason they had ever intersected at all was they'd happened to choose the same compartment on the train that first September. If one were to draw their lives on a map, it would look like a trapezium, like a warped square drawn by a child's unsteady hand, because that's what they were back then, children, and they were children when they died, too.

James was the first one on the train that first day, before even the prefects, because he was good at sneaking around and he'd spent all summer planning a way to get aboard ahead of everyone else. Sure enough, King's Cross was a madhouse, with crying parents and overloaded suitcases and screeching owls occupying every square inch of the place; nobody noticed the small dark-haired boy slip into the cab of the engine. From there he'd ducked between cars until he found the compartments meant for students, and he'd settled into the window seat and peeked out at the other families. He saw his own parents milling around, most likely looking for him, and he felt a twinge of guilt. They'd probably worry. They were like that. He'd have to owl them when he arrived to let them know about this little prank.

More people began to board the train, most of them sporting shiny prefect badges, but eventually regular students filled the aisles. James looked out through the glass compartment door, trying to make eye contact with them. A few of them met his gaze. The first was a pretty redhead who scowled when he winked at her and went back to chatting to her greasy-haired friend. The second was a tall boy with wavy hair and gleaming eyes, who took James' eye contact as a sign that he was welcome to join the compartment.

"Hullo," James said, straightening up. "First year?"

"Give me your seat," the boy replied.

James raised an eyebrow. "Pardon?"

"I said give me your seat. I want to sit by the window."

James smirked. "No."

The boy stepped forward menacingly. "Don't be a dolt, just give me the seat. Before I hex you," he added.

James jutted his chin toward the seat across from him. "There's another window seat right there. And I don't believe you know any hexes."

"I . . ." The boy looked frustrated. "Look, can't you just get up?" he said, dropping his haughty air. "My family's watching - I can see them standing out there - and they told me if I don't try to be more assertive I'll never get into Slytherin, and if I'm not in Slytherin they're going to kill me. Just give me this seat. And maybe cry a little, so it looks like I've bullied you into it."

James shook his head, snorting. "They want you to be in Slytherin?"

"My mum and dad were both Slytherins. So's my cousin. And they're all looking, so would you just get up?"

James grinned. "Sorry, mate. I'm going to be a Gryffindor, like my dad, and we Gryffindors don't bow down to Slytherins. Not even for show. We're braver than that."

The boy groaned, but he let himself collapse in the other window seat. "I'm Sirius," he said glumly. "Sirius Black, for now, although I'm sure I'm about to be disowned."

"James Potter," James replied. "What's so bad about not making Slytherin? Maybe you'll be in Gryffindor with me."

Sirius laughed humorlessly. "They'd probably rather have me end up in Hufflepuff."

The compartment door slid open, and a boy with shabby clothes and a thin face stepped halfway inside. "D'you mind?" he asked, pointing at the empty seat beside Sirius. "Everywhere else is filling up fast."

"Depends," James said, grinning. "Are you a Slytherin? Black here can't associate with anyone who isn't a Slytherin." Sirius kicked him, but he was smiling, too.

"Dunno," the boy replied nervously, coming all the way in. "I haven't been Sorted yet. I'll be a first year. Remus," he added. "Remus Lupin."

"Lupin?" Sirius repeated. "I've never heard of the Lupins."

Lupin sat down gingerly, looking as if he expected someone to yell at him for it. "Erm, sorry?" he said. "It's my surname. I can't help whether you've heard of it or not."

James began to laugh. Sirius scowled. "What house was your dad in?" he asked.

"Ravenclaw."

"And your mum?"

"She wasn't. She's a Muggle."

"Oh." Realization dawned on Sirius' face. "I know what you are!"

Lupin stood immediately. "I'll find a seat somewhere else," he said, face pale.

"You're a half-blood!" Sirius said triumphantly. "That's why I've never heard of you!"

Lupin froze. "Yes," he said slowly.

"Not that there's anything wrong with being a half-blood," James said. "Sit down, Remus. The train's about to move."

Lupin was opening his mouth to reply when something thudded against the glass. "Sorry!" shouted the muffled voice on the other side of the door. "I didn't - I'm sorry!"

Lupin reached over to open the door, and a round boy with watery eyes nearly fell into the compartment. "I didn't mean to," the boy squeaked. "I tripped, I'm so sorry."

"Relax," Lupin told him, smiling. "Do you have a seat yet?"

The boy looked down at the trunk in his hand. "No," he said.

"Sit here," Lupin offered, and the boy's eyes widened.

"Thank you!" he squealed, tugging his trunk out of the aisle and collapsing into the seat next to James. "Thank you so much. We got here late, I wasn't sure I'd be able to make the train."

"What's your name?" James asked while Lupin - and Sirius, when he noticed Lupin needed help - heaved the new boy's trunk up into the overhead luggage rack.

"Pettigrew," said the boy. "Peter Pettigrew." The train lurched to a start; Peter tumbled over into James' lap. "Sorry!" he cried, face growing pink as he hurriedly righted himself. "I'm sorry. I'm dead clumsy. That's why we were late today, I tripped and fell down the stairs." He turned a little pinker when he noticed James start to smirk. "My mother had to make sure I didn't break any bones." He sighed. "Mum says I'll be my own undoing."

"So you'll probably be a Slytherin then, too, if that's the case," James said with a snigger, glancing at Sirius.

"Nope!" said Peter. "Gryffindor, like my mum."

"Gryffindor?" Sirius' face broke into a grin. "You won't be a Gryffindor, mate. Look at you. You're trembling. You apologized to us twenty times before you sat down, and you still look like you're about to cry. Gryffindors are brave, Pete."

"Peter," corrected Peter, but his face was beet red. James slung an arm around him.

"He could be a Gryffindor," argued James. "Gryffindors don't always start off brave. Courage can be learned."

"Yeah," said Peter, glaring at Sirius. "Courage can be learned."

"After all," James continued, "not everyone knows at age eleven that their greatest dream is to die charging into battle!" He held up an imaginary sword and ran it through Sirius, who scowled and looked out the window.

"Die in battle," Lupin repeated dreamily. "That's how I'd like to go, I think."

"Maybe you'll join me in Gryffindor!" James said, and a newly grinning Sirius made a suggestive comment about the two of them stabbing each other with their swords, and the compartment dissolved into laughter-filled conversation that no one but the train itself remembers now.

They never quite made sense together, those four particular boys. How could they, after all, when one was keeping secrets, and one was never good enough, and one wasn't even human? How could they know that as they sat there planning their Sortings, their friendships, their eternities - how could they know that there was no future, that each one was barely more than a minute from the deep end, and that no matter how much they came to love and hate and need each other, it would all be over just as quickly as it began?

Each soul that sat down in that compartment that first September was dead before it could even live: one died running into battle, one was his own undoing, one was destroyed by his family, and one fell to the Slytherin he refused to bow before. One by one they all stumbled through Death's trapezium-shaped trap doors, and the ones left behind were powerless to do anything but wonder.