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- "You did very well to get so far."
- ―The Fat Controller addressing Thomas, Duck and Percy
I am happy to say that Thomas and his friends are still at work, trying as hard as ever to prove themselves to be Really Useful Engines. My father is still taking an interest to the Region's affairs, but it is with grateful thanks that I would like to dedicate this book to him, the person who began it all.
The guard tells Thomas' crew that the stationmaster's house was burgled the previous night, and his gardening trophies and new car were stolen. Thomas is later puffing through the valley when he sees a car very much like the stationmaster's one and warns his crew, who identify the driver and passenger as the thieves. At the next signalbox, they throw the fireman's lunch box, with a note inside, to a signalman. The thieves are stopped at a roadblock, the trophies and car are recovered undamaged, and the Fat Controller arrives at Ffarquhar to congratulate Thomas and his crew.
Tom Tipper the postman falls ill, and, when he recovers, discovers that his van has been replaced with a bicycle. When he gets to Ffarquhar, Tom is asked to fill in some papers, so he props his bicycle carefully against the fence, and asks Percy to keep an eye on it. A boy comes along and starts riding the bike just as Percy starts. The boy falls off and manages to get out of the way, but the bike is run over and is beyond repair. Luckily, all ends well as Tom is given his van again.
An extra load of fish needs to transported in The Flying Kipper, but the only vans available are several old rusty ones. At Wellsworth, Henry calls for a banker and Duck arrives to help him with his train. Going up Gordon's Hill, however, a tail-lamp falls off and Duck drops behind. Henry soon slows down, and Duck collides with the vans, denting his funnel and boiler.
One day after pulling the Express, Gordon feels tired and Thomas replies by telling him to become a tank engine. Later, it is discovered Gordon needs new tubes. Henry is told to pull the Express, but one day he gets sick too. Thomas, Percy and Duck (each of whom starred in one of the book's other stories) are the only engines available, so they are coupled up. On Gordon's Hill, Percy runs out of steam. They're unable to uncouple him, so they try to struggle to the Works. Duck breaks down just outside the station, and Thomas, unable to take the train himself, stops. Gordon, who watched the whole scene from his siding, makes heavy breathing noises at Thomas.
- The Fat Controller
- Tom Tipper
- The Little Boys (do not speak)
- The Thieves
- Mermaid Liverpool (cameo)
- Annie and Clarabel (do not speak)
- Edward (mentioned)
- Bertie (mentioned)
- The Works Diesel (possible mention)
- Hackenbeck Tunnel
- River Callan
- Tidmouth Harbour
- Gordon's Hill
- Crovan's Gate
- The Railway Works
- Elsbridge (mentioned)
- Triple Header was the first story of the four to be written. It is based on an incident at the Nene Valley Railway involving an 0-6-0 named "Thomas". This engine was named by Wilbert Awdry himself, and has been used in special events on said railway.
- Completely by coincidence, the Reverend W. Awdry planned to call his twenty-seventh volume "Really Useful Engines".
- The opening message by the author was slightly altered by Egmont when republished in 2007. In editions from 1983 to 1999, Christopher stated that his father was still taking an interest in the region's affairs, but the 2007 version had this altered due to Wilbert's passing, saying sadly he was no longer involved.
- The first two illustrations of Triple-Header were based on previous Railway Series work: the first on Reginald Payne's second illustration of Thomas and Gordon and the second on C. Reginald Dalby's second illustration of Edward, Gordon and Henry.
- Thomas' valance is curved again.
- In "Mind that Bike", the line to Anopha Quarry has disappeared.
- In "Fish", the line beside the shed at Tidmouth Harbour has disappeared.
- In the second to last illustration, no platform for the Skarloey Railway at Crovan's Gate is visible.
- Thomas varies in size throughout the book.
- In Triple Header, Percy is missing his smokebox saddle.
- Duck's smokebox is green again.