E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Screw Plot (The).
1708, when Queen Anne went to St. Pauls to offer thanks-givings for the victory of Oudenarde. The tale is that the plotters took out certain screw-bolts from the beams of the cathedral, that the roof might fall on the queen and her suite and kill them.