Air date: July 12th, 2016 (UK), October 18th, 2016 (US)
Lord Callan is having a special birthday ball, and Spencer has to take the Duke and Duchess to Callan Castle. The Duke has prepared a speech as well as bringing a present. He reminds Spencer that they must get to the castle on time, and Spencer promises that he will not let them down.
Spencer's first stop is at Knapford, where the Thin Controller has just arrived on his bicycle to have a meeting with the Fat Controller. Mr. Percival tells him that he prefers to ride his bike, as "two wheels are best." Bertie disagrees and thinks that four wheels are best, while Thomas likes his six wheels. Spencer arrives and boasts that twenty wheels are the very best. The Duke reminds Spencer of his job, so Spencer sets off again.
Spencer speeds along confidently, when suddenly his valve gear snaps and he slows to a stop, unable to go on. The Duke begins to worry about being late when Thomas arrives. He teases Spencer about his twenty wheels letting him down, and offers to take the Duke and Duchess the rest of the way to the castle, to which they agree.
But Thomas has not gone very far before he has to stop to avoid hitting a fallen tree. Bertie pulls up, and offers to take the Duke and Duchess himself. As they climb aboard, Bertie boasts that four wheels are best. Bertie hurries towards the castle through the quiet country roads. But suddenly, he runs over some nails laying in the road, and punctures a tyre. The Duke is just about to give up hope when the Thin Controller arrives on his bicycle. The Duke tells him about his important destination, so Mr. Percival sets off to call for help. Soon, Harold arrives to pick up the Duke and Duchess. They quickly climb aboard and Harold flies them to the castle. Lord Callan greets them and asks where Spencer is. The Duke promises to tell him over dinner, and thanks Harold for his help.
That evening at Knapford, Spencer feels very embarrassed for breaking down. But his valve gear has been fixed, and Bertie's flat tyre is mended too. Thomas still does not know how many wheels are the best, while the Fat Controller tries to ride Mr. Percival's bike, but he does not get the hang of it. Harold flies over the station, and Thomas realises that he did not even use his wheels.
This episode contains examples of:
- Butt-Monkey: The Fat Controller.
- Luminescent Blush: Spencer blushes in embarrassment after his valve gear snaps.
- Rule of Three: Spencer's valve gear snaps, Thomas is blocked by a tree, and lastly Bertie runs over some nails, puncturing his tire.
- Shout-Out: Of all things, the title references the much-more kid-unfriendly Animal Farm, of which the phrase "Four legs good, two legs bad" derives from.
