An invitation from the Queen sends Thomas and the Fat Controller heading for London, but the journey is anything but straightforward and Thomas meets a very special engine called Duchess along the way.
Thomas befriends a stray dog who is wandering around the railway and tries to find him a home. In the process, Thomas derails and the fuzzy little dog raises the alarm.
In Brazil, Thomas meets two wood-burning engines who've never travelled beyond their eucalyptus railway. Thomas agrees to swap jobs with them for the day, but this causes more trouble than he expects.
Sonny is trying to prove himself to be a useful engine so that he can stay working on Sodor, but nobody seems to trust him - nobody apart from Diesel, that is. But can Diesel be trusted?
Yong Bao tells Thomas the story of how he cleverly diverted an accident, saving hundreds of passengers and was decorated for his bravery with a tiger emblem on his tender and a bright red coat of paint.
Gordon tries to tell Rebecca how to pull the express like he does, but Rebecca proves that her way may not always be as loud or fast, but works just as well.
In an attempt to beat Thomas in a race, Cleo decides to use the railway lines instead of the road. She soon learns that the roads are much safer for a little car.
Thomas is asked to dress up as a monkey for a special event at the Animal Park, but all the other engines laugh at him. Luckily, Rebecca is on hand to offer some useful advice.
Emily worries she doesn't have a best friend but, when the other engines help her out of a tricky situation, she realises she's been surrounded by best friends all along.
