Heath Ledger’s last screen performance, a remarkable one interrupted by his tragic death at age 28 in 2008, comes wrapped in the kind of passionate provocation of a movie that the Aussie actor favored. Terry Gilliam, the mad visionary behind Brazil, Time Bandits and Monty Python, was ready to scrap the film after the passing of Ledger, who had filmed only the London scenes. As the movie was conceived, Ledger’s con man, Tony, would join the traveling horse-drawn caravan of Dr. Parnassus (a terrific Christopher Plummer) and lead customers behind a mirror to a parallel world of computer-generated fantasy. What saved the film was Gilliam’s decision to call on three of Ledger’s colleagues — Johnny Depp, Jude Law and Colin Farrell — to play Tony in the scenes behind the mirror. Despite a shaky framework, the magic works. It’s a chance to see Ledger one last time in the act of doing what he loved. Take it.