Federal investigators prevented a real-life Halloween horror by busting at least five terror plotters inspired by ISIS in Michigan early Friday, sources familiar with the operation told The Post. Authorities raided three homes in the Detroit suburbs of Dearborn and Inkster and recovered weapons including legally owned guns, the sources said. The alleged plotters spoke of launching a “pumpkin day” assault while they were under round-the-clock FBI surveillance and trained at a local shooting range, the sources said.