- “Well, thank you, my dear. I knew this was my special birthday party, but I didn't know it was fancy dress!”
- ―Lady Hatt greeting her husband
Lady Hatt's Birthday Party is the fourth episode of the fifth season.
One Summer's Day, Bertie asks Thomas and Percy if they have noticed something different about the Fat Controller. Percy tells Bertie that he saw the Fat Controller staring into the clouds this morning and he wonders why. It is Lady Hatt's birthday and the Fat Controller has a new outfit to wear especially for the birthday party. Lady Hatt tells him not to be late and her husband tells her that he will be spic and span and right on time.
The Fat Controller is leaving work early to attend the party at Kirk Ronan. He tells the stationmaster that he will be taking the car when the engines are busy. He thinks it is reliable, but it is not. His mood soon changes when his car becomes stuck in a pothole with a flat tyre. He decides not to risk changing it because it will dirty his suit and it will never do for his wife's party.
The Fat Controller then sees Caroline and explains the situation and hitches a lift in her, but Caroline does not like going fast and she breaks down. George the Steamroller then arrives and insults Caroline, but his driver is more polite to the Fat Controller and offers him a ride to Thomas, who is just down the line, and he agrees, promising Caroline that he will send for help. George enjoys rolling along the road, but not the Fat Controller, who quickly becomes covered in oil. Worse is to follow; George cries for help, slips out of control due to a malfunction, and ends up into a muddy ditch close to where Thomas is taking on water and the Fat Controller catapults and ends up waist-deep in the mud.
Thomas had never seen the Fat Controller in such a mess and he asks Thomas' driver for a ride, but Thomas' fireman had taken ill, so the Fat Controller offers to be Thomas' relief fireman. He works hard and coal dust and soot fly everywhere and at last, Thomas arrives at Kirk Ronan, just in time. The Fat Controller quickly buys a bunch of flowers for the party and as the clock strikes three, the Fat Controller arrives, tired but triumphant. He gives his wife the flowers and she is most grateful and she knew it was her special birthday party, but she did not know it was 'fancy dress'. Everyone laughs and then the party begins.
- Sir Topham Hatt
- Lady Hatt
- Jem Cole (not named)
- James (cameo)
- Mrs. Kyndley (cameo)
- Refreshment Lady (cameo)
- The Butler (cameo)
- The Tailor (cameo)
- Bridget Hatt (deleted scene cameo)
- During the scenes where the Fat Controller rides in his car and Caroline, music is heard in the US and international versions but not the UK version.
- In the UK version, George's whistle is heard earlier than in the US version.
- In the US version, the sounds made by the Fat Controller's car, Caroline and George are barely audible.
- When the Fat Controller arrives at Lady Hatt's party, an instrumental version of the song "Happy Birthday to You" is heard playing in the background.
- This episode marks the first of two things for Lady Hatt:
- Her first speaking role.
- The first time she is referred to by name.
- One of the flowers the Fat Controller buys is really a stem of broccoli.
- This episode marks the last of two things:
- Caroline's last speaking role to date.
- Jem Cole's last speaking role until Journey Beyond Sodor
- In the US, this episode aired before A Better View for Gordon on the Cranky Bugs and Other Thomas Stories VHS/DVD, meaning the viewers would not have known about Gordon's view at Kirk Ronan.
- When Lady Hatt says "I didn't know it was fancy dress," one of the people laughing is missing their eyebrows.
- The narrator says that George was enjoys "rolling along the lane," but he still looks cross. In the same scene, wires are visible on George.
- Jem Cole does not have any eyebrows.
- When the narrator says, "Later that day, the Fat Controller changed into his new suit," the Fat Controller is missing one of his eyebrows.
- When Sir Topham Hatt looks all over the car, he gets any eyebrows.
- For the rest of the episode after George crashes, the Fat Controller does not have eyebrows.
- When Thomas wishes "Good Luck!" to the Fat Controller, his driver's small scale model is wearing glasses even though the model did not when Thomas starts going to the station.
- It is said that Caroline spluttered with fury, but she looks very sad.
- Jem Cole disappears when the Fat Controller falls off George.
- In a rare picture, Caroline's driver is smiling when she breaks down.
- When George cries "Help! Something snapped!" the Fat Controller is elevated a bit in George's cab.
- When George crashes, the Fat Controller's model prematurely tips over.