Anyone who’d spent any time at all at Number 12 Grimmauld Place in the past weeks would not have been surprised to see an identical pair of ginger heads creeping down a creaky staircase at ten minutes past one o’clock on a July morning.

Fred and George Weasley were intrepid explorers of the dusty mansion they currently occupied, having thoroughly scoured the premises for anything that could alleviate the boredom of being stuck in a safe house with their parents, younger brother, and sister—not to mention a former convict, a sickly werewolf, and a tetchy ex-Auror.

Tonight, though, they had a different mission. It was, in fact, a professional excursion, designed to test a handy little item they’d concocted right under their mother’s annoyingly watchful eye using bits of string and some very clever (if they said so themselves) charms.

They planned to run their experiment in the narrow hallway outside the kitchen, where they knew Sirius and Remus would be talking and sharing their habitual nightcap after everyone else was safely abed.

The teenaged entrepreneurs were heading down the stairs, treading slowly and carefully to avoid detection.

A cracking sound pierced the heavy silence, halting the pair in their tracks.

“Shhh!” hissed George (or was it Fred?)

“I can’t help it if the step creaks,” whispered the other one.

They stayed as still as if they’d been Petrified, listening for the squeak of their parents’ bedroom door opening, dreading their mother’s triumphant shriek of discovery.

When neither came to pass, they heaved a tandem sigh of relief and continued their journey.

As they were about to descend the next flight of stairs, a sound came from behind a door next to them, and they froze again, certain they were about to be caught this time, brought down by the constant vigilance of the man whose room it was.

But the door didn’t fly open, and the muffled noise inside the room continued. As if in mute agreement, they crept closer and put their ears to the door.

A pair of voices murmured inside.

The boys looked at one another, eyebrows raised.

Fred pointed at the pocket of his brother’s dressing gown.

George shook his head and pointed back at his brother.

“I don’t have—” Fred started to whisper, but George clamped a hand over his mouth, glaring at him and gesturing insistently at the door.

Fred glared back at George and reached over into George’s pocket.

He pulled out a long, flesh-coloured bit of string. He looked pointedly at George.

George rolled his eyes and nodded.

Gingerly, Fred fed the end of the string under the crack beneath the door. The boys leant over the other end.

They were rewarded with the sound of a familiar voice, now clear enough to make out the words.

“… have a wash-up.”

There was the creak of a light tread, then the squeak of a door closing.

The brothers made a silent and simultaneous fist-pump.

It works! Fred mouthed, his eyes bright with excitement.

They leant down again, trying to hear more.

There was only a frustrating silence, punctuated by the painfully loud sound of someone clearing their throat.

Then, sweet success!

The interior door creaked again, and the first voice said, “What on earth did you do to me? My knees are still weak.”

“I like me witches with weak knees.”

“Lucky thing, then,” said the woman. “Budge over.”

There was the brief, high-pitched protest of a bedspring.

“’Night, Min.”

“Goodnight.”

The thin shaft of light under the door winked out.

The eavesdroppers looked at one another, identical grins spreading across their faces.

They waited another minute, huddled over the string, then George shrugged, withdrew it, and put it back in his pocket. He pointed to the ceiling, and they headed back up the stairs to their room, the echoes of victory and discovery ringing sweetly in their ears.