Step 1: Look for the fixed expression that goes with "conspiracy." English uses "hatch a plot" or "hatch a conspiracy" to describe secretly devising a plan, drawing on the image of an egg hatching into something fully formed. Step 2: "Prepared a conspiracy" and "made a conspiracy" are understandable but not natural collocations, and "cooked" is informal and imprecise here. Step 3: Replacing "cooked" with "hatched" gives the standard idiomatic phrase. \[\boxed{\text{Hatched}}\]