Peter III was an idiot. Plain and simple. His wife, Catherine would have tried to over-through him one way or another and probably succeed. In his six month reign, Peter managed to piss off the nobility, the church, and the army. He changed the army uniforms to the hated Prussian colors, tried to take the lands of the church and I'm not sure what he did to piss of the nobles but it was probably tied into the army. Not to mention he planned a war with Denmark over the Duchy of Holstein, a pointless war. He also abolished the secret police, a popular move, but made t even easier to plot against him. Al and all, if there wasn't a plot against Peter in 1762 then there would have been one at a later date.