Caitlin is a fast streamlined engine from The Other Railway, who was designed for speed. She also has her own set of coaches painted in a similar colour scheme to her own.
Along with Connor, Thomas, Percy and James, she helped with the search of Stephen before Ulfstead Castle's opening. Caitlin once had to spend the night on Sodor and became 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.