Louise Brealey (born 27 March 1979), also credited as Loo Brealey, is an English actress, writer and journalist. She played Molly Hooper in Sherlock, Cass in Back, Scottish professor Jude McDermid in Clique and Gillian Chamberlain in A Discovery of Witches. On stage, Brealey has received widespread critical acclaim for starring in productions at the Royal National Theatre, Royal Court Theatre, the Young Vic, and the Bristol Old Vic, directed by Sir Peter Hall and Marianne Elliott. (Via Wikipedia)