Percy and Harold/Percy Takes the Plunge is a Ladybird book based on the second season episodes, Percy and Harold and Percy Takes the Plunge. It is illustrated using photographs from the television series.
While working at the harbour with Toby and Thomas, Percy meets a helicopter named Harold at a nearby airfield. Harold tells Percy that he thinks railways are slow and out of date. Later, after collecting his trucks from the quarry, Percy sees Harold flying overhead and races him to the harbour. Percy wins the race and Percy's fireman sings a song about the race. While at the harbour shed, Percy speaks to Bill and Ben about his adventure in the flood. Henry comes in and sends the twins away. Percy says that water is nothing to an engine with determination and puffs away. Later, Percy sees Thomas looking at a danger sign beyond the quay. Percy is unaware of the sunken foundation of the quay and tries to pass it many times, but all of his attempts fail. Then, Percy asks the trucks to bump him at the quay. The trick works and Percy falls into the sea. The Fat Controller scolds Percy and sends some cranes to lift Percy out of the sea. The next day, Percy is sent to the works on Henry's good train.
- Images from the episodes Percy and Harold, Percy Takes the Plunge, Thomas and Gordon, Dirty Objects, Trouble in the Shed, Duck Takes Charge, Pop Goes the Diesel, and Daisy are used.
- A cassette tape narrated by Ringo Starr was included with some of the books.
- Bill and Ben are referred to by name unlike in the actual episode.