- “Engines don't swim, Henry - you were meant to deliver fish, not swim with them. You should know that by now.”
- ―Sir Topham Hatt scolding Henry
Thomas is at the quayside and is about to take vans full of fish to Brendam Docks for Henry's train, The Flying Kipper. The fishermen, however, are using old equipment, and Thomas begins to worry about being late. Then, a crate of fish drops onto his boiler, spilling fish all over him. His driver and fireman laugh, but Thomas sniffs at the pongy smell.
Later, he travels along the Coastal Run, but he is furthered delayed by a man. Thomas stops, and the man informs him and his crew about some tracks eroded from high tides, and he has marked the spot. The driver decides to go inspect, and they set off. Soon, they arrive at the unsafe area. The tracks are safe enough for Thomas, but they can not bear the weight of a heavy engine like Henry. The guard places a red lamp pole by the damaged track as a warning spot to engines, and states that he will tell the signalman at the Docks to close the line.
It is already dark once Thomas arrives at Brendam Docks, with Henry waiting for him. He is cross with Thomas being late and smelly. Thomas warns Henry of the danger, but Henry does not listen to Thomas' warnings and has Thomas get his trucks hitched to the train. Finally, the Flying Kipper is away.
Inside the yard master's office, the yardmaster tells Thomas's crew that he is taking the Coastal Run; this shocks the driver, as he already told the yardmaster of the danger to big engines. The yardmaster quickly phones the signalman to reroute Henry, but Henry passes the signal box before the signalman can be warned, anxious to make up for lost time. Once Henry reaches the coastal track, however, a thick fog rolls in, and neither he nor his driver can see the track ahead. By now, the damaged track has been completely submerged, and Henry plunges into the sea with his train, coming to a stop offshore.
By the next day, the tide is high enough for Henry and his fish to be rescued from the water. When Henry is put in a barge full of fish, the Fat Controller scolds him, saying that engines are supposed to deliver fish, not swim with them, which he should know. Henry is brought back to the Docks by barge to be lifted back onto dry tracks. Cranky expects Henry will have some "fishy" tales to tell, but then some children laugh at Henry and call him a green whale, then a monster. Henry is most upset.
Finally, Henry is back on the rails, and Thomas feels sorry for him. He comes to take him away for a washdown. After being cleaned, Henry apologises to Thomas for being rude to him. Thomas accepts Henry's apology, then jokes with Henry about smelling something--fresh air.
- Sir Topham Hatt
- The Lighthouse Keeper (not named)
- James (cameo)
- Big Mickey (cameo)
- The inspiration partly for this episode may have come from the magazine story, A Fishy Smell.
- This episode marks the last appearance of The Flying Kipper until the sixteenth season episode Whiff's Wish, excluding two stock footage appearances in the seventh season.
- In the UK version when Thomas says "I can't help it, it's the fish!" the steam appears forward, then is played backwards, then played forwards again, meaning that the film was cut, but edited.
- After Henry reaches the fog, he loses two vans.
- Before Henry falls into the sea, his brakes are applied and his wheels stop moving, but when he runs into the sea, his wheels are moving again, despite the braking sound effects still being audible.
- When Thomas puffs away with Henry at the end of the episode, the puffing noise starts long before Thomas moves.
- In the US version, when Henry says "I can't see!" the first horn "honk" is barely audible.