Invert!

While they were on the run, Harry and Hermione did some brainstorming on how to hide a house. The magical tent was useful, but had its limits. And the Fidelius was hard to cast, and also meant that friends (and the mailman) would have to be brought into the secret. So with a little arithmancy and spell-crafting from Hermione, and some well-thought-out suggestions and extra power from Harry, the two invented the Invert! Spell. It would turn an above-ground house into a below-ground one, and the two together had enough power and finesse to do it with some ease.

First they tested it out on some abandoned properties. They needed to iron out the kinks: how to hide the surface, either with grass or a patio? How to provide a hideable entrance and stairway leading down? How to provide normal daylight, sunlight and breezes to come through the house's windows, even though they were now underground? Not to mention, how to safely vent the fumes from gas stoves and cookers, and fireplaces? And the trickiest: how to keep electric and water lines hooked up, and provide proper drainage for waste water, even though the underground house was now lower than the sewer lines? By the fifth abandoned house, they had worked it all out – and it was almost good enough to move into, though people in the nearby village had noticed the sudden disappearance of the old Baker cottage, and were snooping around – so they had to move on.

When they arrived outside #12 Grimmauld Place, they had Kreacher scout inside and make sure no hostiles were present. Once it was declared all clear, they cast Invert!, with all its new subtle variations – and, like a pair of trousers being turned inside out, the whole house slowly disappeared underground. The success was complete, and had the advantage of being in London, being a whole big house with a full kitchen and many bedrooms, and yet still having the property be invisible to the neighbors, thanks to the lasting Fidelius charm on it. They moved in, and soon noticed another advantage: like a cave, the house was now cooler in the daytime, and warmer at night.

The pair offered the new charm to the Weasleys to hide the Burrow, but Molly simply wasn't having it. They did convince the nearby Lovegoods, and their rook-like home was now well-hidden; and they let the Weasleys know that it could be accessed as a safe house if needed. Now that they had mastered the charm, they created several more safe-houses around the country from abandoned properties – just in case.


After the war was finished, Harry began remembering his mischievous pranking Marauder heritage, and showed up at the Dursleys' house. He'd become adept enough at the charm to do it himself – and just as well, because Hermione would not have approved when he stuck his wand out from the invisibility cloak, and chanted, Invert! And #4 Privet Drive disappeared below ground. Uncle Vernon came storming up, red-faced, from what seemed like a bomb shelter or root cellar, and yelled at what seemed an empty lot, "Boy! You put this back immediately! I'm warning you!"

"Oops," Harry muttered to himself very softly, "Forgot to develop the counter-charm!" And apparated away with a very soft Pop.