It’s elementary for Downey Jr.

Robert Downey Jr. is trading “Iron Man’s” metal suit for Sherlock Holmes’ deerstalker hat.

Downey is following his action blockbuster “Iron Man” with the title role in “Sherlock Holmes,” a mystery drama based on Arthur Conan Doyle’s detective and an upcoming comic book about Holmes by Lionel Wigram, one of the movie’s producers.

Guy Ritchie is directing the Warner Bros. film, which is set to begin shooting in October, the studio said Thursday. That should put it ahead of the schedule for a “Sherlock Holmes” comedy in development at Sony, which will star Sacha Baron Cohen as the detective and Will Ferrell as Dr. Watson.