The phrase "diabolical plot" refers to a wicked, evil or extremely sinister plan or scheme that is deliberately crafted with harmful intentions. Full definition
In a seemingly diabolical plot, veterinarians and pharmaceutical companies have teamed up in a scare - mongering marketing campaign to frighten guardians into giving year - round heartworm preventatives to their cats. (littlebigcat.com)
And Carbone is already scheming more diabolical plots to come. (entrepreneur.com)
And even though Lex Luthor's diabolical plot remains relatively undeveloped in comparison to the love story, Kevin Spacey manages to play his character with a nasty kind of glee. (parentpreviews.com)