The term COMPLEX PLAN can be broken down into two crossword solutions, PLOT and SCHEME. A PLOT is a plan or strategy to achieve a goal, usually involving a series of steps. It is often used in literature to refer to the sequence of events that make up a story. A SCHEME is a plan or program of action, usually with a specific purpose or goal in mind. It is often used to refer to a plan that is more elaborate or intricate than a PLOT. Together, these two words can be used to describe a complex plan that involves multiple steps and a specific goal.