The Missing Christmas Decorations is the nineteenth episode of the seventeenth season.
Plot
The diesels are upset that the steam engines have loads of decorations at Tidmouth Sheds. Diesel 10 decides to steal some, despite Sidney's attepmts at persuading him that he himself is a decoration. The steam engines are upset to see their decorations gone, until Percy discovers Diesel 10 stealing the supplies! He chases him back to the Dieselworks, joined by the rest of the steam team along the way. Here they also discover poor forgotten Sidney hanging from the ceiling waiting for new wheels. Percy surprises the other engines by giving Sidney a special Christmas present and teaches everyone about the generous spirit of Christmas.