Caitlin is a streamlined engine from the Mainland designed for speed. She loves to challenge the other engines to a race and has a tendency to get a little-overexcited. She, along with Connor, regularly transport passengers from the Mainland to Ulfstead Castle.
Caitlin once had to spend the night on Sodor and become too excited to listen to advice. During her night on Sodor, she took the mail train and the Flying Kipper. Unfortunately, she did not take others into consideration and ended up waking lots of people up.