Thomas boasts of how his blue paintwork looks splendid. But he doesn't look so splendid when he gets covered in coal dust whilst working at the Coal Hopper! Percy laughs at his friend's accident, but it's not long before he has a mishap with coal too!

Old Edward unknowingly loses part of his train due some bothersome cows who break out of their field and cause a coupling to come loose. He feels very cross when Henry and Gordon laugh about it and boast that cows wouldn't bother them. However, they'd reckoned without Bluebell the cow!

In a lonely, rusty Scrapyard is poor Trevor the Traction Engine, who is ready to be broken up. He is feeling sorry for himself because he feels that he's too old-fashioned to be Useful. Edward finds Trevor's situation to be a tremendous shame, and is determined to find someone to buy Trevor and save him, but who would "have room for a Traction Engine at home?"

Some boys fiddle with James's controls and he trundles off down the line by himself. It is up to Edward to catch up with James and allow James's fireman to jump aboard the runaway engine to stop him.

Trevor is getting bored, but Edward has good news. The Fat Controller wants Trevor to help with his new Harbour. Edward takes Trevor to the Junction, where the Traction Engine meets Thomas. Thomas takes him down to the Harbour, but has his doubts as to how useful Trevor can be since he doesn't run on rails. Thomas is soon pleasantly surprised.

Percy has been playing tricks on the bigger engines, such as telling Gordon he is late for his train and telling James he mustn't leave the shed because an Inspector is coming to visit. Gordon and James want their revenge, and so come up with a plan to trick Percy, by brainwashing him with the ludicrous idea of "backing signals"...

Percy is ill of the bigger engines around ordering him about. The Fat Controller releases him to work at his new Harbour, and also brings in a new engine called Montague, but who prefers the name of "Duck". The big engines try and order Duck around as well, but Duck won't stand for it and together with Percy, he puts them in their place.

Percy is enjoying his new work at the Harbour. The line is near an airfield, where a boastful helicopter called Harold lives. He reckons that, "Railways are slow and quite out of date!" But Percy proves a point when he challenges Harold to a race...

Thomas is feeling unwell, so Edward takes him to the Works to be repaired. Whilst Thomas is away, Duck fills in for him and is very popular with Annie, Clarabel and the passengers. When Thomas comes back, he resumes his duties. However his handbrake hasn't been fixed properly by the workmen and one day the Fireman forgets to pull it hard enough. As a result, Thomas and the coaches "run away", and only Harold and an Inspector can help stop the runaway train.

Percy brags that "Water is nothing to an engine with determination!" But he feels very foolish when he learns that you can't trust trucks and takes an unfortunate dip!

Duck is boasting about being Great Western and how useful he is, much to the annoyance of the others. Later, the Fat Controller introduces Diesel, a shunter who is "on trial". He asks Duck to show Diesel around, but Diesel says he doesn't need Duck. Duck leaves him to it and Diesel has an accident with some trucks. He thinks it's Duck's fault...

Diesel is still angry at Duck, and plans his revenge. He tells the trucks jokes about Gordon, James and Henry, and says Duck told them to him. The trucks start gossiping, and soon enough the big engines find out...

Duck has been sent to work with Edward for a while, and tells Edward that the Fat Controller and the other engines all hate him. Edward says they don't, and asks Duck if he would like to help him work. Duck helps Edward pull a heavy goods train up Gordon's Hill, but the trucks break away and speed down the line. Duck manages to control them but a barber's shop is up ahead...

The viaduct is being repaired on the Main Line. The Fat Controller doesn't want to close the railway whilst the repairs are being done, and so orders the mainliners to go slowly when crossing it. This delays them with their journey to Thomas, which makes him late to meet with Bertie. Altogether, Thomas becomes very annoyed; until the day comes when he realises that being late isn't such a bad thing after all.

Donald & Douglas have arrived from Scotland to help the Fat Controller - but have caused great confusion in that only one engine was expected! Despite all, they try their best but a spiteful brake van causes trouble between them.

The engines are worried that Donald & Douglas might be sent away after their accidents. Edward suggests that they hold a Deputation - and poor Percy gets the task to tell the Fat Controller about it!

For many years, Thomas the Tank Engine has run his well-known branch line, and knows just where to stop. "You could almost manage it without me!" jokes his Driver. What a surprise Thomas gets when he tries to do so and pays the Stationmaster an unexpected visit!

Thomas's recent accident has caused a great deal of trouble. The Fat Controller decides to send for a Diesel Railcar called Daisy to help Percy and Toby "while Thomas is... ummm... indisposed!" But poor Percy and Toby have a hard time when Daisy becomes difficult and bitter.

Percy grumbles about taking the milk when Daisy doesn't bother to do so. Toby offers him to swap jobs; he takes the milk and Percy fetches his trucks. However, Percy becomes rather cocky and soon finds himself in trouble with runaway trucks and a breakvan in the way...

Bill & Ben are twins who work at the China Clay Pits. One day, they are aghast when they discover that their trucks have gone missing! Down the line, they cause great problems and difficulty with a diesel called Boco, who they believe stole the trucks. Confusion regains until Edward explains everything.

Since the arrival of Boco, Gordon is upset when the Fat Controller allows branch line diesels to pull main line trains. Edward suggests that he should run on the branch for a change. Gordon thinks such an idea "vulgar", but little does he know that a run on the branch is quite unexpectedly in store that night...

Henry, Gordon and James are teasing poor Edward about being too old and "how he should be preserved before it's too late." Duck and Boco tell them to "Shut up!" as "Edward's better than any of you!"; and during a serious breakdown on an important journey, Edward proves his worth once and for all.

Percy tells Thomas and Toby a story about a ghost train. Thomas doesn't believe it and says Percy is a "silly little engine". Percy's Driver later tells him it wasn't true, it was on television. Later that night, Percy is on his way back from the Harbour when he crashes into a lime cart trapped on a crossing. Now white as a sheet, and with help from Toby, Percy heads off to find and scare Thomas...

During the summer, Percy likes to help the harvesters by delivering their bales of hay to Toby, who takes them to the farms, to feed the animals. Unfortunately, Percy makes Thomas very late and cross indeed. Percy doesn't care until a crate of treacle and a hay storm cause some embarrassment...

The Fat Controller sends Thomas to fetch the Christmas Tree for the Christmas party, but on the way back he gets stuck under a big snowdrift. No-one knows what has happened to Thomas, so Donald & Douglas go out to look for him. Will Thomas get home in time?