The Hidden House is believed to be a noble House or mystical force alleged to have existed by some merchant lords of Abah's Landing in the Second Era during the rule of Princess Magnifica Falora.
After the Merchant House Crisis of the 2E 560s, many came to believe that there was a force in the shadows that brought about the hardship. This took the form of the 'Hidden House', as some claimed that it seemed as though an unknown merchant House had entered Abah's Landing. While some took this metaphorically, others took it literally, believing a family was secretly planning the downfall of Abah's Landing.
Others claimed that what was called the 'Hidden House' was a mystical force that brought ills upon the merchant lords, with some commoners believing it was divine punishment for their opulent and excessive lifestyles.
Quotes
Like the vast chasm in front of you in the middle of the night, you can feel the Hidden House's presence looming in the darkness, even though you can't see it.
—Tamonir about the Hidden House in his Abah's Landing's Merchant Lords
The Gouges shant be a threat any longer, the Hidden House saw to that.
—X at-Addin about House Gouges