Episode VII: Engine Unknown was uploaded on January 24, 2014 and is the seventh episode of the first season.
A mysterious engine rushes past others in tunnels and night without revealing himself, leading to the engines to wonder who it could be.
- Pip and Emma
- Sir Handel
- Peter Sam (does not speak)
- Stanley (cameo)
- Derek (cameo)
- Hiro (cameo)
- Ivo Hugh (cameo)
- Diesel 10 (cameo)
- Stepney (cameo)
- Spencer (cameo)
- Den (cameo)
- Sidney (cameo)
- Paxton (cameo)
- Rosie (cameo)
- Mallard (tender cameo)
- Duck (mentioned)
- Oliver (mentioned)
- Scruff (mentioned)
- Smudger (mentioned)
- Skarloey (indirectly mentioned)
- RightonTracks10: Thomas
- EnterprisingEngine93: Edward
- Andrew Homer: BoCo, Duke and James
- Knapford Productions: Bear and Bertie
- DarthWill3: Diesel
- Thomas1Edward2Henry3: Everyone Else
- This episode marks the first appearance of KnapfordProductions as Bertie and Bear as well as Andrew Homer as Boco and Duke.
- Events from the Railway Series books Very Old Engines and Henry the Green Engine are referenced.
- Music from the movie The Lord of the Rings: The Fellowship of the Ring is used.
- Because this episode has a cliffhanger ending that ties into the next episode, this is the first episode not to have the traditional Thomas outro at the end.
- This episode has the most cameos.
- As of September 2016, this is the most viewed episode of The Engines of Sodor with over 600,000 views.
- Towards the end of the episode, Neil mentions that it has been 170 years since his time began. However, he was built in 1856 and would have been 158 years old in 2014.