The phrase "devilish plan" is correct and usable in written English.
You could use it to describe a particularly diabolical or evil plan that someone is attempting to carry out. For example, "The criminal mastermind had a devilish plan to rob the bank."
"French President Sarkozy Sold Out His Ally Turkey in a Devilish Plan! Denial Bill Passed the Senate.
It will, however, presumably welcome Taiwan's continued restraint unless it fears a devilish plan to reach statehood inch by inch and committee by committee.
Voter suppression didn't work in November, and it may even have backfired in some states, so they just devised another devilish plan.
The human becomes a demon, whInh is itself an allegory of war: "You become a demon, you stay that way".
Like most of the world I just spent eight hours of my life binge watching Queer Eye, whilst sobbing sporadically and also trying to hatch some sort of devilish plan to get them all to be my best friends.
Our pain is immense, but everyone should be assured that our unity and togetherness will spoil these devilish plans in our country and abroad".
And perhaps there are furrowed brows at Google's Mountain View headquarters as they worry about their neighbours' devilish plans to run off with the lucrative search advertising market.
But with each additional detail that Nasdaq has provided about the plan, the more devilish some investors think it has become.
The point about September 11th was not its detailed planning; not its devilish execution; not even, simply, that it happened in America, on the streets of New York.
Was it destiny's plan, or part of a devilish deal?
There is devilish pleasure in watching the doctor put his plan into motion, but there are hints that this is more than a sales job.
