Popish Plot
1678. Supposed conspiracy by Roman Catholics to kill the Protestant Charles II of England and replace him by his Roman Catholic brother, James, Duke of York.
Principal item of the plot was a manuscript written by Titus Oates and Israel Tonge that pretended the Roman Catholic Church to approve of the assassination of Charles II by English Jesuits. The alleged plot resulted in an anti-Catholic frenzy, in which 24 Catholics were executed for treason and several others died in prison. The eventual discovery of the plot preceded the Exclusion Crisis.
Sources:
http://dspace.dial.pipex.com/town/parade/abj76/PG/pieces/popish_plot.shtml