- Lara Pulver - Irene Adler
- Tanya Moodie - Ella
- Amanda Abbington - Mary Morstan
- Deborah Moore - Crying Woman
- Lynn Farleigh - Professor Cairns
- John Sessions - Kenny Prince
- Zoe Telford - Sarah
- Di Botcher - Connie Prince
- Doug Allen - Joe
- Haydn Gwynne - Miss Wenceslas
- Lars Mikkelsen - Charles Magnussen
- Sharon Rooney - Laura
- Amelia Bullmore - Dr Stapleton
- Russell Tovey - Henry Knight
- Clive Mantle - Dr Frankland
- Ed Birch - Tom
- Lindsay Duncan - Lady Smallwood
- Stephen Wight - Fletcher
- Toby Jones - Culverton Smith
- Simon Kunz - Sir Edwin
- Sacha Dhawan - Ajay
- Marcia Warren - Vivian
- Eleanor Matsuura - DI Hopkins
- Charles Edwards - David Welsborough
- Amanda Root - Emma Welsborough
- Rob Callender - Charlie Welsborough
- Georgina Rylance - Cornelia
- Gina Bramhill - Faith
- Art Malik - Prison Governor
- Timothy Carlton - Mr. Holmes
- Wanda Ventham - Mrs. Holmes
- Matthew Needham - Bezza
- Debbie Chazen - Vicky
- Miranda Hennessy - Reporter
- Siobhan Hewlett - Helen
- Indica Watson - Little Eurus
- Will Sharpe - Corporal Lyons
- William Scott-Masson - Sir Jeffrey Patterson
- Yasmine Akram - Janine
- Alistair Petrie - James Sholto
- Victoria Wicks - Margaret Patterson
- Ruth Everett - Political Aide
- Syrus Lowe - Political Aide
- Katy Maw - Beth Davenport
- Ben Rufus Green - Reporter
- Imogen Slaughter - Reporter
- David Nellist - Mike Stamford
- Gemma Chan - Soo Lin Yao
- Louise Breckon-Richards - Jennifer Wilson
- Al Weaver - Andy Galbraith
- Lisa McAllister - Anthea
- Stanley Townsend - Angelo
- Bertie Carvel - Seb Wilkes
- Peter Brooke - Taxi Passenger
- Daniel Percival - Eddie Van Coon
- Paul Chequer - DI Dimmock
- Phil Davis - Jeff
- Howard Coggins - Brian Lukis
- Janice Acquah - Museum Director
- Jack Bence - Raz
- John Macmillan - Community Officer
- Olivia Poulet - Amanda
- Jacqueline Chan - Shopkeeper
- Sarah Lam - Opera Singer
- Gillian Elisa - Surgery Receptionist
- Stefan Pejic - Box Office Manager
- San Shella - Alan West
- Caroline Trowbridge - Mrs Monkford
- Paul Albertson - Mr Ewart
- Rita Davies - Blind Lady
- Stefano Braschi - Raoul
- Jeany Spark - Homeless Girl
- Alison Lintott - Julie
- John Lebar - Golem
- Joanna Burnett - Tour Guide
- Danny Webb - DI Carter
- Andrew Havill - The Equerry
- Todd Boyce - Neilson
- Oona Chaplin - Jeanette
- Richard Cunningham - Timid Man
- Rosemary Smith - Married Woman
- Simon Thorp - Businessman
- Anthony Cozens - Geeky Young Man
- Munir Khairdin - Creepy Guy
- Luke Newberry - Young Policeman
- Darrell Las Quevas - Plummer
- Rosalind Halstead - Self / Kate
- Peter Pedrero - Archer
- Simon Paisley Day - Major Barrymore
- Gordon Kennedy - Gary
- Kevin Trainor - Billy
- Rosalind Knight - Grace
- Chipo Chung - Presenter
- Katherine Parkinson - Kitty Riley
- Tony Pitts - Chief Superintendant
- Jaye Griffiths - Prosecuting Barrister
- Ian Hallard - Defence Barrister
- Malcolm Rennie - Judge
- Sydney Wade - Claudie Bruhl
- Paul Leonard - Bank Director
- Christopher Hunter - Prison Governor
- Tony Way - Prison Warder
- Sian Brooke - Elizabeth
- Sian Brooke - Eurus Holmes
- Lorraine Hilton - Miss Mackenzie
- Peter Basham - Reporter
- Robert Benfield - Gallery Director
- Ifan Huw Dafydd - Clerk of the Court
- Michael Müller - Father
- Pano Masti - Assassin
- Douglas Wilmer - Diogones Gent
- Alfred Enoch - Bainbridge
- David Fynn - Howard Shilcott
- Tomi May - Torturer
- Rick Warden - Bonfire Dad
- Trixiebell Harrowell - Zoe
- Jim Conway - Reporter
- Nicole Arumugam - Reporter
- David Gant - Mr. Szikora
- Robin Sebastian - Mr. Harcourt
- Derren Brown - Derren Brown
- Alice Lowe - Tessa
- Oliver Lansley - David
- Jalaal Hartley - Photographer
- Adam Greaves-Neal - Page Boy
- Helen Bradbury - Mum
- Tim Chipping - Duty Sergeant
- Will Keen - Major Reed
- Ritu Arya - Gail
- Georgina Rich - Charlotte
- Wendy Wason - Robyn
- Nicholas Asbury - Landlord
- Tom Brooke - Bill Wiggins
- Calvin Demba - Isaac Whitney
- Tim Wallers - John Garvie
- Glen Davies - Chauffeur
- Brigid Zengeni - Kate Whitney
- Matthew Wilson - Security Man
- Honor Kneafsey - Girl on Plane
- Honor Kneafsey - Little Girl
- Louis Oliver - Little Sherlock
- David Newman - Medic
- Katherine Jakeways - Benji
- Will Ashcroft - Club Waiter
- Gabrielle Glaister - Ambassador
- Harry Gostelow - Husband
- Richard Syms - Vicar
- Neal Barry - Ray Kingsley
- Andrew Bone - Jack Sandeford
- Albert Magashi - Karim
- Daniel Hoffmann-Gill - Gold Teeth Man
- James Holmes - Plane Passenger
- Eiry Thomas - Stewardess
- Aleksandar Mikic - Guard
- Hattie Ladbury - Female Client
- Martin Savage - Ivan
- Katy Wix - Nurse Cornish
- Eric Kofi Abrefa - Policeman
- Lee Knight - Reporter
- Asheq Akhtar - Saheed
- David Kirkbride - Hospital Policeman
- Usman Akram - MI5 Agent
- Dominic Borrelli - Husband
- Eileen Dunwoodie - Wife
- Samantha E. Hunt - Amy Saunders
- Richard Crehan - Ben
- Ralph Ineson - Vince
- Clare Foster - Velma
- Brett Allen - Special Unit Guard
- Rhys Rusbatch - Technician
- Paul Weller - The Viking
- Arthur Conan Doyle
- Sue Vertue
- Bethan Jones
- Steven Moffat
- Rebecca Eaton
- Beryl Vertue
- Mark Gatiss
- David Arnold
- Michael Price
Catherine McCormack hace el papel de Lady Carmichael.
Rosalind Knight interpreta a Grace en la serie.
Benedict Cumberbatch hace el papel de Sherlock Holmes.
Martin Freeman interpreta a John Watson en la serie.
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