Perfect Percy is a magazine story.
One day, Percy and Diesel are shunting trucks in the main station yard when Diesel rolls by Percy and spills oil on his track. Percy splashes through the oil which causes his to slide along out of control. Percy collides with some buffers and sand spills out of one of his trucks.
Soon, the Fat Controller arrives and sees Percy's wheels half-buried in sand. Percy tries to explain that it isn't his fault, but the Fat Controller isn't interested. He tells Percy that he has to behave or be taken out of service. Percy feels very cross indeed.
The sand is soon cleared up and both engine resume work. Percy wants to teach Diesel a lesson. Meanwhile, Diesel is misbehaving and going too fast. This causes one of his trucks to break loose and roll towards Percy who angrily gives the runaway truck a bump.
The Fat Controller is inspecting the coal chute. He hears the noise and sees the truck rolling towards him. The Fat Controller jumps out of the way of the runaway truck as it speeds past the chute. Next moment, a huge heap of coal falls out exactly where Sir Topham had been standing. The truck says that Percy bumped him on purpose. Percy thinks he is in trouble again, but the Fat Controller is happy; the coal would've hit him had he not sent the truck to warn him. Then, Diesel is told off for being careless and Percy is pleased with the way things have turned out.
- According to the final illustration, a truck could not go under the hopper where the Fat Controller was standing because there is a line of trucks already in front of the hopper.