The book Christopher Awdry claims was the most difficult for him to write, sympathising with the trouble his father went through writing James the Red Engine!  A turning point for James as a character, as he goes through a transistion and realises that Diesels aren't such bad characters after all, in spite of his own previous perceptions and misgivings.

Old Stuck-Up
An arrogant visiting Diesel is put in his place by an unfortunate accident in the yard, following rather rude comments made about the engines in Old Stuck Up.  He soon learns his lesson after crashing through the wall of the engine shed when trying to be cleaned and refuelled, but only happening to slip on the oily rails left by Boco and Bear previously!
 
Crossed Lines
James is full of himself and moaning about Diesel engines, claiming they wouldn’t know which way they were going owing to their two cabs in Crossed Lines.  He’s soon made to rethink his words when he’s forced to make a trip in thick fog across the yard with a few flat trucks.  When an engine’s whistle dumbfounds a signalman, James is sent sliding across two lines and crashing into a signal!
 
Fire Engine
A discussion on colour in the shed sparks a heated debate between Henry and James, and the following day leaves Henry in the unfortunate position of having to have his fire thrown out to avoid overheating, following the uncoupling of his tender from his main body.  Following, he was less inclined to make rude comments on the colour of Fire Engines!
 
Deep Freeze

During the Deep Freeze, the grips of winter get the better of James when he has to fill his water supply and ends up getting more than he bargained for as it overspills onto his tender.  This in turn causes his injector to fail and leads to him having to be rescued by a Diesel from the Works.  Unsure of the new comer at first, James and he are soon chatting away like old friends, and by the end, James’ view on Diesel engines has changed for the better.