Series 21

The twenty-first series of Thomas & Friends started airing on 18th September 2017.

Production
Originally, the twenty-first series of Thomas & Friends was written for a full twenty-six episode series, but due to the delayed productions of the nineteenth and twentieth series after The Adventure Begins was fast-tracked into Arc Productions' schedule, eight of the episodes were cancelled so that development of Big World! Big Adventures! and the twenty-second series could begin. At the time, it was unknown what the cancelled eight episodes were about, but according to Sodor Island Fansite/Forums, one of the episodes would have been about Rosie. Then, in March 2021, producer Ian McCue confirmed that the episodes Confusion Without Delay, Samson and the Fireworks (originally Oliver's Fear of Fireworks), Thomas' Animal Ark, Chucklesome Trucks, and Nia and the Unfriendly Elephant were all originally written for the twenty-first series. These episodes were pushed back to the twenty-second, twenty-third, and twenty-fourth series respectively. McCue also stated the The Christmas Coffeepot and Over the Hill were to be exclusive to the Tinsel on the Tracks DVD, hence why they were not broadcast with the rest of the twentieth series, and were instead broadcast with twenty-first series. Later, in July 2022, Sam Wilkinson confirmed that the episode, The Case of the Puzzling Parts was also written for the twenty-first series.

Characters

 * Thomas
 * Edward
 * Henry
 * Gordon
 * James
 * Percy
 * Toby
 * Donald and Douglas
 * Emily
 * Harvey
 * Spencer
 * Rosie
 * Belle
 * Stephen
 * Porter
 * Glynn
 * Ryan
 * Diesel
 * Daisy
 * Mavis
 * 'Arry and Bert
 * Salty
 * Den
 * Dart
 * Paxton
 * Sidney
 * Philip
 * Flynn
 * Skarloey
 * Victor
 * Luke
 * Millie
 * Rex
 * Bert
 * Annie and Clarabel
 * Henrietta
 * Troublesome Trucks
 * Judy and Jerome
 * Bertie
 * Kevin
 * Harold
 * Cranky
 * Big Mickey
 * Reg
 * Sir Topham Hatt
 * Lady Hatt
 * Stephen Hatt
 * Bridget Hatt
 * The Thin Clergyman
 * The Fat Clergyman
 * Dowager Hatt
 * Farmer McColl
 * The Mayor of Sodor
 * Lord Callan
 * The Duke and Duchess of Boxford
 * The Photographer
 * Sir Robert Norramby
 * The Grumpy Passenger
 * Sir Topham Hatt's Brown-haired Assistant
 * The Bird Watcher
 * The Tree Specialists
 * Albert's Wife
 * Little Thomas
 * The Female Puppet Show Entertainer
 * Farmer Finney
 * Skiff
 * Rocky
 * Sir Topham Hatt's Blond-haired Assistant
 * Mike
 * Duck
 * Bill and Ben
 * Stanley
 * Charlie
 * Caitlin
 * Norman
 * Stafford
 * Winston
 * Rheneas
 * Sir Handel
 * Peter Sam
 * Slip Coaches
 * Trevor
 * Butch
 * Jack
 * Oliver the Excavator
 * Max and Monty
 * Owen
 * Jem Cole
 * Fergus Duncan
 * The Foreman
 * Mr. Bubbles
 * Captain Joe
 * The Teacher
 * Sodor United Football Team
 * The Search and Rescue Manager
 * The Blond-haired Boy
 * The Ginger-haired Boy
 * One of Dowager Hatt's Friends
 * The Welsh Bird Watcher
 * The Lady with the Big Hat
 * The Great Railway Show Judge
 * The Ffarquhar Stationmaster
 * The Man with the Green Waistcoat and Grey Hair
 * Farmer Trotter
 * Daisy's Fitter
 * Oliver
 * Flying Scotsman
 * Hiro
 * Connor
 * Gator
 * Timothy
 * Marion
 * Samson
 * Ashima
 * Axel
 * Raul
 * Shane
 * Yong Bao
 * Gina
 * Theo
 * Lexi
 * Diesel 10
 * Ivan
 * The Mainland Diesels
 * Hugo
 * Etienne
 * Rusty
 * Duncan
 * Toad
 * Bradford
 * The Climbers
 * Stepney
 * Whiff
 * Cyril the Fogman

Returning Characters

 * Terence
 * Bulgy

Characters Introduced

 * Hannah
 * Carly
 * The Sea Serpents
 * Rebecca
 * Nia

Locations

 * Island of Sodor
 * Arlesburgh
 * Arlesburgh Goods Yard
 * Arlesburgh Yard Shed
 * Arlesburgh Harbour
 * Arlesburgh Maritime Museum
 * Arlesburgh West
 * Arlesburgh West Shed
 * Blue Mountain Quarry
 * Brendam Docks
 * Brendam Warehouse
 * Sodor Shipping Company
 * Bridge Over Tunnel Runby
 * Callan Castle
 * Conrad's Bridge
 * Crosby Tunnel
 * Crovan's Gate
 * Skarloey Engine Sheds
 * Crowe's Farm Crossing
 * Dryaw
 * Dryaw Airfield
 * Dryaw FC
 * Duck Pond
 * Farmer Trotter's Pig Farm
 * Ffarquhar
 * Ffarquhar Quarry
 * Mavis' Shed
 * Gordon's Hill
 * Hackenbeck Tunnel
 * Terence's Field
 * Harwick
 * Kellsthorpe Road
 * Knapford
 * Annie and Clarabel's Shed
 * Knapford Yards
 * M.C. Bunn
 * Neptune Refreshments
 * Sir Topham Hatt's Office
 * Maithwaite
 * Maron
 * McColl Farm
 * Rail Under Road Bridge and Signalbox
 * Road and Rail Runby and Road Bridge
 * Sodor Search and Rescue Centre
 * Sodor Steamworks
 * Victor's Shed
 * Suddery Junction
 * The Sheep Field
 * Tidmouth Sheds
 * Tidmouth Engine Works
 * Tidmouth Goods Station
 * Tower Windmill
 * Ulfstead Castle
 * The Dinosaur Park
 * Ulfstead Mine
 * Ulfstead Sheds
 * Vicarstown
 * Vicarstown Bridge
 * Vicarstown Dieselworks
 * Diesel 10's Shed
 * Vicarstown Tunnel
 * Vicarstown Diesel Sheds
 * Wellsworth
 * Crocks Scrap Yard
 * Wellsworth Bridge
 * Wellsworth Sheds
 * Wellsworth Yards
 * Black Loch
 * Bluff's Cove
 * Knapford Sheds
 * The Duke and Duchess of Boxford's Summer House
 * Tidmouth
 * Topham Hall
 * Three-Track Level Crossing
 * Sodor Animal Park
 * The Mainland
 * The Mainland Craneworks

UK

 * John Hasler as Thomas
 * Keith Wickham as Edward, Henry, Gordon, Harvey, Glynn, Salty, Den, Skarloey, Bert, Bertie, Harold, the Fat Controller, Dowager Hatt, Farmer Finney, Lord Callan, the Great Composer, the Grumpy Passenger and the Woodsmen
 * Nigel Pilkington as Percy and a Passenger
 * Rob Rackstraw as James, Toby, Donald, Flynn, Big Mickey, the Thin Clergyman and the Red Sea Serpent
 * Joe Mills as Douglas
 * Teresa Gallagher as Emily, Belle, Mavis, Annie, Clarabel, Judy, Stephen Hatt, Bridget Hatt, the Duchess of Boxford, the Blond-haired Boy, Albert's Wife and the Lady in the Yellow Dress and Hat
 * Kerry Shale as Diesel, 'Arry, the Troublesome Trucks and Kevin
 * Nicola Stapleton as Rosie
 * Matt Wilkinson as Spencer, Cranky, Kevin, the Duke of Boxford, the Dock Manager and the Bird Watcher
 * William Hope as Iron Bert and Farmer McColl
 * Bob Golding as Stephen and Sidney
 * Tracy-Ann Oberman as Daisy
 * Steven Kynman as Porter, Ryan, Paxton and Dart
 * David Bedella as Victor and the Mayor of Sodor
 * Michael Legge as Luke
 * Mike Grady as Sir Robert Norramby
 * Miranda Raison as Millie
 * Tim Whitnall as Jerome and Reg
 * Maggie Ollerenshaw as Henrietta
 * Tom Stourton as Rex, Terence and the Fat Clergyman
 * Rasmus Hardiker as Philip and the Troublesome Trucks
 * David Menkin as Porter
 * Lucy Montgomery as Hannah and Carly
 * Colin McFarlane as Bulgy and Bertie's driver
 * Ian McCue as the Blue Sea Serpent
 * Christopher Ragland as the Troublesome Trucks

US

 * Joseph May as Thomas
 * William Hope as Edward, Toby, Iron Bert, Farmer McColl, the Duke of Boxford and the Dock Manager
 * Kerry Shale as Henry, Gordon, Diesel, the Troublesome Trucks, Harold and Kevin
 * Rob Rackstraw as James, Donald, Flynn, Big Mickey, the Thin Clergyman and the Red Sea Serpent
 * Christopher Ragland as Percy and the Troublesome Trucks
 * Joe Mills as Douglas
 * Jules de Jongh as Emily and the Duchess of Boxford
 * Keith Wickham as Harvey, Glynn, Salty, Den, Skarloey, Bert, Bertie, Sir Topham Hatt, Dowager Hatt, Lord Callan, Farmer Finney, the Great Composer, the Grumpy Passenger and the Woodsmen
 * Teresa Gallagher as Belle, Mavis, Annie, Clarabel, Judy, Stephen Hatt, Bridget Hatt, the Blond-haired Boy, Albert's Wife and the Lady in the Yellow Dress and Hat
 * Glenn Wrage as Spencer and Cranky
 * Nicola Stapleton as Rosie
 * Bob Golding as Stephen and Sidney
 * Tracy-Ann Oberman as Daisy
 * Steven Kynman as Ryan, Paxton and Dart
 * David Bedella as Victor and the Mayor of Sodor
 * Michael Legge as Luke
 * Mike Grady as Sir Robert Norramby
 * Miranda Raison as Millie
 * Tim Whitnall as Jerome and Reg
 * Maggie Ollerenshaw as Henrietta
 * Tom Stourton as Rex, Terence and the Fat Clergyman
 * David Menkin as Porter
 * Rasmus Hardiker as Philip and the Troublesome Trucks
 * Lucy Montgomery as Hannah and Carly
 * Colin McFarlane as Bulgy
 * Ian McCue as the Blue Sea Serpent
 * Nigel Pilkington as a Passenger

Trivia

 * Every episode has a copyright of 2017.
 * Arc Productions had produced the first seven episodes and Terence Breaks the Ice before their bankruptcy.
 * This series contains the 500th episode of the show, P.A. Problems.
 * This series marks the third of two things:
 * The third series not to have Thomas' name titled in any of the episodes, the first being the fifteenth series and the second being the twentieth series.
 * The third series to not introduce any new engines (not counting Hannah and/or Carly). The first being the eighth series, and the second being the fifteenth series. Though Rebecca was intended to be introduced in this season.
 * This series marks the first of several things:
 * The first series to have no episodes written by Andrew Brenner during his tenure as head writer.
 * The first series to be produced by Mattel Creations.
 * The first series not to have Togo Igawa as part of the voice cast since his return in King of the Railway.
 * The first series not to have Jonathan Forbes, Olivia Colman, Jamie Campbell Bower and John Schwab as part of the voice cast since they joined the voice cast in the seventeenth series, Tale of the Brave, Sodor's Legend of the Lost Treasure and The Great Race, respectively.
 * Ian McCue's first series as creative executive and the first series to have him as part of the voice cast.
 * Micaela Winter's first series as producer for the series.
 * Sukhmani Kaur's first series as assistant production manager.
 * Zahara Andrews' first series as production coordinator.
 * Alan Kennedy's first series as director of post-production.
 * Ryan Quaglia's first series as post-production editor.
 * Gavin Ebedes' first series as supervising editor.
 * Terence, Bulgy and Farmer Finney's first appearances in full CGI.
 * Hackenbeck Tunnel, Terence's Field and Suddery Junction's first appearance in full CGI.
 * Big Mickey's first appearance with a face in the television series.
 * The first series where Caitlin appears without Connor.
 * The first series in which where Duck, Caitlin and Mike appear, but do not speak since their introductions.
 * The first series since their returns in where Peter Sam and Butch appear, but do not speak.
 * The first series in which Hiro, Scruff, Connor, Marion, Samson, Hugo and Bradford do not appear since their introductions.
 * The first series in which Oliver, Whiff, Toad and Alfie do not appear since their returns.
 * The first series since the fifteenth not to introduce any new engines.
 * The first series to feature Rosie without her original lavender livery.
 * The first series since the sixteenth to have all of its episodes released in the same year.
 * The first series to have episodes fully animated by Jam Filled.
 * The first series not to be dubbed in Dutch since the twelfth series.
 * The first series not to be dubbed in German since the seventh series.
 * The first series not aired on JimJam and Minimax since the twelfth series.
 * The first series where the engines and vehicles perform non-static movements and are able to move their bodies around. This would become more prominent after Journey Beyond Sodor was finished and then next Series 21.
 * The first of three series (two if counting mini-specials) not to have an episode with that series' number per series in it, due to there only being 18 out of 26 episodes in this series that made it past the storyboards. These include, as follows (so as to avoid confusion):
 * Thomas and Gordon as the first episode of Series 1 (and also the very first ever episode overall).
 * Cows as the second episode of Series 2.
 * Time for Trouble as the third episode of Series 3.
 * You Can't Win as the fourth episode of Series 4.
 * James and the Trouble with Trees as the fifth episode of Series 5.
 * The Fogman as the sixth episode of Series 6.
 * James and the Queen of Sodor as the seventh episode of Series 7.
 * Thomas, Emily and the Snowplough as the eighth episode of Series 8 (Edward the Great, if going by production order).
 * Thomas and the Toy Shop as the ninth episode of Series 9 (Bold and Brave, if going by production order).
 * Seeing the Sights as the tenth episode of Series 10 (Topped Off Thomas, if going by production order).
 * Smoke and Mirrors as the eleventh episode of Series 11 (Thomas and the Lighthouse, if going by production order).
 * James Works it Out as the twelfth episode of Series 12.
 * Thomas and the Runaway Kite as the thirteenth episode of Series 13.
 * Thomas' Crazy Day as the fourteenth episode of Series 14 (Thomas and the Snowman Party, if going by production order).
 * Big Belle as the fifteenth episode of Series 15.
 * Whiff's Wish as the sixteenth episode of Series 16.
 * No Snow for Thomas as the seventeenth episode of Series 17 (The Switch, if going by production order).
 * Last Train for Christmas as the eighteenth episode of Series 18 (Spencer's VIP, if going by production order).
 * The first part of Diesel's Ghostly Christmas as the nineteenth episode of Series 19 (The Little Engine Who Races Ahead, if going by production order).
 * Useful Railway as the twentieth episode of Series 20 (Blown Away, if going by production order).
 * Rosie is Red as the twenty-second episode of Series 22 (Hunt the Truck, if going by production order).
 * This is the only series for a few things:
 * The only series in which Willie does not appear since his introduction in the previous series.
 * The only series since their returns in where Bill, Ben, Max and Monty appear, but do not speak.
 * The only series where Stafford, Rheneas and Oliver the Excavator appear, but do not speak since their introductions or reintroductions respectively.
 * The only series in which Farmer Finney has a speaking role, but was never referred by name.
 * The only series not to have an episode featuring Percy as the main character.
 * This series also marks the last of several things:
 * Mark Moraghan's last series as narrator for the UK and US dubs.
 * The last series to have Michael Legge as part of the voice cast and the last series where he voices Luke.
 * The last series to utilise the original storytelling format.
 * The last series to use the Engine Roll Call as the title music.
 * The last series to use the newly updated new series theme.
 * Boris Andreev's last series as art director.
 * Alan Kennedy's last series as post-production supervisor.
 * Gavin Ebedes' last series as editor.
 * The last series to have Helen Farrall as part of the writing team.
 * The final series in which the Steam Team consists of all eight of its original members.
 * The final series to have Edward, Henry and Toby as members of the Steam Team, as well as the former two as main characters.
 * The final series to have an episode where Thomas is not featured at all. From the twenty-second series onwards, he appears and narrates every episode (the latter on a permanent basis).
 * The final series where Donald, Douglas, Spencer (excluding fantasy sequence appearance), Mavis, Stafford and Rheneas appear, although Stafford is mentioned in the twenty-fourth series episode, Kenji on the Rails Again.
 * The last series until the twenty-fourth series to not feature any fantasy sequences for several episodes.
 * The last series to use the Engine Roll Call on a regular basis.
 * The last series to air on Family Jr. in Canada. Treehouse TV in Canada took over from the twenty-second series onwards.
 * The last series not dubbed in Norwegian, Swedish, Danish and Finnish.
 * The last series to have episodes released on home media in the United States of America.
 * The last series to air its episodes within one year in the United Kingdom.
 * The last series aired by KBS 2 in South Korea.
 * The last series narrated by Kim Seung-jun in South Korea.
 * The last series to have Baek Kyung-hoon and Lee Je-in as part of the voice cast in South Korea.
 * The last series recorded and mixed by An Ho-sung in South Korea.
 * The last series translated by Kim Hye-yeon in South Korea.
 * The last series directed by Lee Won-hee in South Korea.
 * The last series to have Korean subtitles.
 * The last series aired by CBeebies in Poland.
 * This is the shortest series of the main series, with a total of only 18 episodes. Originally, a full 26-episode series was planned, but eight episodes were cut to make way for the development of Big World! Big Adventures! and the twenty-second series. In addition to this, Sodor Island Forums confirmed that the reduced total of episodes was needed to make up for the delayed productions of the nineteenth and twentieth series, due to The Adventure Begins being fast-tracked into Arc Productions' schedule.
 * At least one of the cancelled episodes would have been about Rosie.
 * In March 2021, Ian McCue confirmed that the episodes Confusion Without Delay, Samson and the Fireworks (originally Oliver's Fear of Fireworks), Thomas' Animal Ark, Chucklesome Trucks, and Nia and the Unfriendly Elephant were all originally written for the twenty-first series, however they were pushed back to the twenty-second, twenty-third, and twenty-fourth series respectively. He has also stated the The Christmas Coffeepot and Over the Hill were to be exclusive to the Christmas on Sodor DVD, and were considered part of the twenty-first series.
 * This is the second series for two things:
 * The second series not to be dubbed at all in Dutch, the first being twelfth series.
 * The second series to have some UK recordings released in the US, the first being the first series.
 * This series has the least dubs in other languages.
 * This series was never dubbed in European Spanish, Italian, Romanian, Dutch, German, Hungarian, Slovenian, Serbian, Croatian, Czech and Greek.
 * In the Estonian, Latvian, Lithuanian, Baltic Russian and Vietnamese dubs, UK dub can be heard in the background as a dubbing track was not used.
 * In the Korean dub, the original British and American production crew were never credited.
 * In Estonian, Latvian, Lithuanian, Polish, Baltic Russian, Turkish, Indonesian, Thai, Chinese Mandarin, Taiwanese Mandarin and Cantonese dubs, credited Mark Moraghan as the narrator, even though they were re-dubbed in their respective languages.