Episode The Final Problem Adaptation: Sherlock Episode: 4x03 Airdate: 15 January 2017 IMDb: The Final Problem (link not verified) Previous: The Lying Detective Cast Benedict Cumberbatch as Sherlock Holmes Tom Stoughton as Young Sherlock Martin Freeman as Dr. John H. Watson Mark Gatiss as Mycroft Holmes Una Stubbs as Mrs. Hudson Rupert Graves as DI Greg Lestrade Andrew Scott as Jim Moriarty Amanda Abbington as Mary Morstan Aaron Richards as Young Mycroft Richard Crehan as Ben Simon Kunz as Sir Edwin Indica Watson as Little Eurus Stuart Jason Lee as Armed Guard Brett Allen as Special Unit Guard Sian Brooke as Eurus Holmes Louise Brealey as Molly Hooper Tam Mutu as Leonard Honor Kneafsey as Girl on Plane Grant Crookes as Police Officer Matt Young as Young Police Officer Art Malik as Prison Governor Timothy Carlton as Sherlock's father Wanda Ventham as Sherlock's mother Rhys Rusbatch as Technician Clare Foster as Velma Harry Tuffin as Victor Paul Weller as The Viking Ralph Ineson as Vince