Elementary is a contemporary, New York-set re-imagining of Sir Arthur Conan Doyle's 19th-century tales about brilliant British sleuth Sherlock Holmes. The show stars London-born actor Jonny Lee Miller as Holmes and Liu as his partner in crime-solving, Joan Watson.
Welsh actor Rhys Ifans, who plays the show's recurring character Mycroft -- Sherlock's brother -- also returned for the episode.
"Business becomes personal for Sherlock when he is forced to partner with his estranged brother, Mycroft, to solve a case with life-or-death consequences," a synopsis of the episode said.
CBS recently announced it renewed the series for a third season.