A Friend's Party is a magazine story.
Stephen and Bridget are going to their friend William's birthday while the Fat Controller takes an afternoon off, but Lady Hatt needs to help the Vicar of Wellsworth with the upcoming Sunday fête, so he takes his grandchildren to their friend's house. Unfortunately, a leaky tap in the bathroom is delaying William's party. The Fat Controller agrees to fix the leaky tap while William's mother sorts out the food, and lends the magician his top-hat for the party performance. The Fat Controller stays for the party and even tells the children about his engines. Afterwards, he declares that going to the party was much better than spending his afternoon off relaxing.