- “Now what did i come in here for again?"
- "Your FLATBED!"
- "Oh yeah.”
- ―Sidney and Dart
The Case of the Puzzling Parts is the twenty-third episode of the twenty-second series.
Sidney has a flatbed with some parts that are needed, but he forgets why the parts are needed. Paxton decides that he and Sidney should be special agents to find out what they are for, they found out from Thomas that the parts are for a diesel engine. While they are searching for more clues to find, Sidney starts to have a few problems with himself and after Paxton points out that he has a wonky horn, a broken lamp, a faulty buffer and coughing up black smoke, both diesels realise that the parts are for Sidney himself.
- Diesel (does not speak)
- Scruff (cameo)
- Luke (cameo)
- Merrick (cameo)
- Owen (cameo)
- Bill and Ben (stock footage)
- Timothy (stock footage)
- Salty (stock footage)
- Cranky (stock footage cameo)
- Big Mickey (stock footage cameo)
- Vicarstown Dieselworks
- Wellsworth Scrap Yard
- Road and Rail Runby and Road Bridge
- Tower Windmill
- Whiff's Waste Dump
- Blue Mountain Quarry
- Sodor China Clay Company (stock footage)
- Brendam Docks (stock footage)
- Sodor Shipping Company (stock footage)
- Joseph May as Thomas
- William Hope as Whiff
- Keith Wickham as Skarloey
- Steven Kynman as Paxton and Dart
- Bob Golding as Sidney
- Tim Whitnall as Reg
- At the end of the episode, Thomas mentions the events of the eighteenth series episode, Timothy and the Rainbow Truck. Stock footage from said episode is also used.
- This episode marks Whiff, Scruff, Timothy, Dart and Luke's (not counting stock footage) only appearances in the twenty-second series as well as Sidney and Skarloey's only speaking roles in the twenty-second series.
- Paxton breaks the fourth wall once again in this episode, as does Sidney.
- When Thomas backs away from Paxton and Sidney, he makes no puffing sounds.
- Throughout the episode, Sidney's wheels moved slower than the speed he was travelling at.
- Nick Jr's captions misspell Sidney as Sydney throughout the episode.