Green’s Dictionary of Slang

addle-plot n.

a spoil-sport who ‘addles’ the ‘plots’ or plans of others.

[UK]D’Urfey Boarding School A2: Dramatis Personae [...] Lady Addleplot, A Lust flaunting imperious Lady, a highflown stickler against the government.
[UK]B.E. Dict. Canting Crew n.p.: Addle-plot, a Martin-mar-all.
[UK]Grose Classical Dict. of the Vulgar Tongue.
[UK]J. Caulfield Blackguardiana.
[UK]Lex. Balatronicum.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.
[UK]R. Milward Man-Eating Typewriter 38: [F]ash bats and sharpering-omis were after us, those evil eagle-eeked addle-plots who cruised the city.