The BBC television series Sherlock has 13 episodes, including its standalone special.
The programme consists of four series, each containing three regular episodes, for a total of 12 standard episodes. It also includes “The Abominable Bride,” a special episode broadcast between series 3 and series 4. Adding that special produces the commonly cited total of 13 episodes.
The counting can cause confusion because “The Abominable Bride” was broadcast as a special rather than as one of the regular series episodes. The programme therefore has four series and one special, not thirteen regular episodes. The series premiered in 2010 and concluded with its fourth series in 2017.