Mischief Night (or 'mischievous night' in the local slang) is celebrated on November 4th, the night before Bonfire Night, mainly in Yorkshire, where the Gunpowder Plotters originated. It refers to the filling of Parliament's cellars with gunpowder on the 4th (being mischievous), ready for detonation on the 5th, when King James I opened Parliament in 1605.