Helena Bonham Carter has signed on to play the mother of Sherlock, Mycroft and Enola Holmes in a new film about Sherlock’s younger sister.

She will star alongside Millie Bobby Brown in Enola Holmes, an adventure project based on the Enola Holmes Mysteries book series by Nancy Springer.

The series, which began with The Case of the Missing Marquess in 2006, is made up of six books and tells the tale of Sherlock and Mycroft Holmes’ much younger sister, Enola, who turns out to be a highly capable detective in her own right.

The film’s script has been written by Jack Thorne.