Guest Stars Rupert Graves as DI Lestrade Una Stubbs as Mrs. Hudson Mark Gatiss as Mycroft Holmes Andrew Scott as Jim Moriarty Stephen Wight as Fletcher Will Sharpe as Corporal Lyons Sasha Behar as Dr Mortimer Rosalind Knight as Grace Russell Tovey as Henry Knight Chipo Chung as Presenter Amelia Bullmore as Dr Stapleton Clive Mantle as Dr Frankland Gordon Kennedy as Gary Kevin Trainor as Billy Simon Paisley Day as Major Barrymore Sam Jones as Young Henry