The phrase "concocted plan" is correct and usable in written English.
It can be used to describe a plan that has been carefully devised or fabricated, often with a sense of creativity or deceit.
Example: "The detective uncovered the villain's concocted plan to steal the priceless artifact."
Alternatives: "fabricated scheme" or "devised strategy".
Parents, many of them unable to return to their homes since the disaster struck, reacted to the hastily concocted plans with both relief and trepidation.
Mr. Padilla, the memo says, is an associate of Al Qaeda who, in travels to Afghanistan and Pakistan, met with senior Qaeda officials, trained in wiring explosives, "researched" dirty bombs, concocted plans for attacks on the United States and, "it is believed," returned to the United States to "conduct reconnaissance and/or attacks" on behalf of Al Qaeda.
Aubrey, who desperately wants Shelah to leave her home and come live with him (nearly an hour's drive away), has concocted plans for a surprise birthday party for his mother which will be attended by her best friend, Mae (Kimberly Scott), her physician (James Carpenter), and her stepdaughter, Cookie (Nikkole Salter).
But miles from ground zero, residents are concocting plans to deal with potential nightmares.
Yet Mr. Carlson was already concocting plans for more ambitious tours, or maybe an all-ages club someday.
In a speech at Northwestern University law school in Chicago, he described al-Awlaki as concocting plans to kill Americans but he never explicitly acknowledged the administration responded by targeting the cleric.
Summer, however, has concocted a plan to circumvent this problem.
I deposited my bags and concocted a plan.
After rain washed out a doubleheader, Giants manager Leo Durocher concocted his plan.
Chicago have concocted a plan to break their time-tested mold and are making steady progress.
