The twenty-first series of Thomas the Tank Engine and Friends is confirmed to air sometime in 2017-2018. It, like the previous three seasons, will have a total of 26 episodes - the last six would initially be DVD-exclusive.
- Little Engines - Percy is tired of being called little, until he finds engines smaller than him and realises he is not small after all.
- Terence Breaks the Ice - Terence the Tractor gets stuck in a frozen lake while delivering a Christmas tree.
- Emily in the Middle - Emily finds herself in the middle of Donald and Douglas' bickering, and must find a way to put a stop to that.
- Surprise Visitor - Gordon is lonely until he sees a familiar face right next to him. Who could it be?
- Paparazzi - Hugo, the rail zeppelin, is getting fed up with being constantly harrassed by the press. Unfortunately, Flying Scotsman is also a victim of the paparazzi, and thousands of unsuspecting people wander onto or beside the tracks just to see him speeding along the line!
- The Big Freeze - When a big blizzard hits the Island of Sodor, it's up to Devious Diesel to help save the day.
- Rosie's New Look - Despite her unique livery, Rosie still feels that she is unpopular. She gets her chance when she asks the Fat Controller for a new coat of paint, so as to be more popular.
- Wizard! - Harold the Helicopter praises Merlin, the Invisible Engine, on account of his daring escape from the scrapyard. This sort of praise made Merlin a little too puffed up in his smoke box. He was told that wizards can make things disappear with a touch of his magic wand. He soon uses his chimneys to make other engines - and himself - "disappear", and tries his tricks on little Philip, who ended up re-appearing in his sight.