No one knows who is taking the Steamies' Christmas decorations from Tidmouth Sheds. Until Percy discovers Diesel 10 stealing them and chases him back to the Dieselworks, where he also discovers poor forgotten Sidney hanging from the ceiling waiting for new wheels. Percy surprises everyone by deciding to give Sidney a Christmas present and his kindness does not go unrewarded. Thomas is sent to bring a real sleigh for Sir Topham Hatt to ride in when he plays Santa at the Ulfstead Castle Christmas Fair. When the sleigh slips down the hill with Sir Topham Hatt in it, Thomas has to rescue him and ends up pulling the sleigh back up the hill with fallen branches round his funnel, making Thomas look more like a reindeer than an engine!