Charles reacted with understandable concern and in the weeks that followed as investigations were launched and arrests made to identify the imaginary conspirators, anti-Catholic hysteria built across England.
This explains the Gunpowder Plot which was foiled on the 5th of November 1605 when Catholic plotters had aimed to blow up parliament during its first sitting, attempting to kill King James I in the process.
The defining features of the conspiracy theory are: the conspirator, the conspiratorial plan — the sinister plan that they're trying to bring about — and the means of mass manipulation by which the conspirator is keeping the plan secret.