It was the year 1965 on the Island of Sodor. The Fat Controller frowned as he looked at the reports from the manager at the Crovan's Gate Works. "So Duck's boiler ticket has expired and he'll be undergoing an extensive overhaul? Then I'll have to let my other engines know before going to see if I can acquire a new engine to fill in for Duck until he's back in service again."

But the Fat Controller knew he could not just cancel all trains for the purpose of calling his engines to Crovan's Gate. So he made a couple phone calls, first he called the controller of the Skarloey Railway so he would be informed of Duck's overhaul. Then, the Fat Controller did the same thing with the Culdee Fell Railway.

Word tended to spread quickly on the Island of Sodor, this became evident when even the engines on the Culdee Fell Railway and the Skarloey Railway were talking about in between breaks where they rested until taking their next train. Soon, the Fat Controller prepared to temporarily leave the Island of Sodor for a trip to the mainland so he could look at possible new engines to fill in for Duck during his overhaul.

After a trip that went on for several hours, the Fat Controller arrived at a goods yard where a long green diesel electric locomotive was busy shunting trucks together to make both passenger trains and goods trains that would be ready for the other engines by the time they got back to the yard.

The Fat Controller smiled at this as he watched the busy locomotive at work. Once all the trains had been sorted and prepared, the engine noticed that there was a visitor to the goods yard. "Hello there sir," the engine said. "What brings you to this goods yard today?" He asked. Hearing this, the Fat Controller made his way over to the diesel electric and looked at his face for a couple seconds before looking around.

"Is there someone in charge of this yard that I can talk to about something?" The Fat Controller asked. The engine told him about some yard officials from British Rail in an office that were currently on their lunch break and he made his way over. Knocking on the door, the Fat Controller found one of the doors open for him. "Sorry to bother you all during your lunch break, but I was looking for an engine so I could give them a trial for a couple weeks."

One of the men pointed out the green diesel he talked to earlier and he nodded while making his way over. Upon learning the name of the engine, the Fat Controller looked up at him. "Say BoCo, I was wondering if you would like to stay on the Island of Sodor for a couple weeks while you undergo a trial. If everything goes well, then I'll purchase you and you'll be a permanent part of the engine fleet for the North Western Railway. And don't worry, your controller said it was alright since he has other engines that can cover for you."

Hearing this, BoCo smiled as the Fat Controller went off to sign some papers for BoCo's controller. After being woken up, BoCo was coupled up to Daisy so the stout gentleman who would be giving him a trial for a couple weeks could see how he handled pulling another engine. With a single blast on his horn, they set off back for Sodor.

"I should warn you ahead of time. Back in 1957, I gave a diesel shunter a trial but he ended up causing trouble for some of my engines. So their initial reaction to you may be a bit, harsh." Listening to what his temporary controller said, BoCo frowned and began to worry about how they would react to him being on the island. After many hours, BoCo and Daisy made it back to Sodor.

Arriving at Crovan's Gate, BoCo's driver gently braked the diesel electric to a stop at the platform. Once he was on the station platform, he smiled in appoval. "A very smooth ride BoCo, and you pulled Daisy along without any trouble at all. Now before you undergo the trial, I want you to head to the works so the staff can check you over for any issues that might have happened on the way here." BoCo was then uncoupled from Daisy and headed to the works pointed out to him by the Fat Controller.

Reversing into the works, his driver stopped him by a green class 57xx pannier tank from the former Great Western Railway. In 1948, the Big Four underwent nationalization to form British Railways, as it was known at the time before being called British Rail starting in 1965. The Big Four that formed British Rail consisted of The Southern Railway, The London, Midland and Scottish Railway, The London and North Eastern Railway, and the Great Western Railway.

Opening his eyes, the tank engine known as Duck looked at BoCo with a suspicious expression on his face as he recalled the memories of what Devious Diesel had done back in 1957. Ignoring BoCo's friendly greeting, Duck would have gladly steamed out of the works had his fire not been put out in preparation for his eventual overhaul. Frowning at this, BoCo felt a little hurt that Duck was ignoring him.

After the workmen checked him over, BoCo glanced around for a few seconds as he was slowly driven out of the works by his driver. But he stopped upon noticing that the Fat Controller was waiting for him. "Now BoCo, I think that you should become better acquainted with the engines of the Skarloey Railway since you're still new to the Island of Sodor."

"Of course, sir," BoCo replied. The Fat Controller then smiled in response.

"That's a good engine, off you go then!" Moving out of the works, BoCo passed over the points and began heading towards the station located at Crovan's Gate. About a minute after he stopped at the station, BoCo heard a horn and glanced at the narrow gauge tracks on the other side of the station, soon noticing a small black diesel stopping at the platform with a maintenance train behind him.

"Hello," the diesel said. "You must be new here, since I've never seen you around before. I'm Rusty, and you are?"

"I'm BoCo. Erm, I'm not trying to come across as rude or anything. But is it normal for engines to be so small?" Rusty would have been offended by this, but he realized that BoCo didn't yet know about narrow gauge.

"Well, I was built to operate on the Skarloey Railway, which is a narrow gauge line. We might be a lot smaller, but that doesn't mean we can't be useful like you bigger engines. Which reminds me, there's going to be a centennial celebration for Skarloey and Rheneas since they're both now 100 years old."

A minute later, Rusty's driver said something to the small diesel and he glanced at BoCo. "Sorry, I've got to go head towards Lakeside and repair some of the line. But maybe I'll see you around again sometime." With a blast of his horn, Rusty set off again and gradually disappeared around the corner as he began heading towards Lakeside with the maintenance train.

But Duck had seen everything from the works, and suddenly felt uncertain about his silent treatment towards BoCo. "Maybe I shouldn't have been so distant towards him. He doesn't even seem to act like Diesel at all, which is a welcome relief from most diesels acting like they're superior to steam. Besides, it's not exactly the Great Western Way to judge another engine before getting to know them."

Duck then began thinking about how Henry, Gordon and James had been turned against him by Diesel, and the diesel on loan from the Other Railway who insulted the engines during Stepney's visit in 1962 before getting his comeuppance by accidentally having an inspector's bowler hat end up stuck in his air intake.

A few minutes before he was due to depart the platform, BoCo noticed the Fat Controller approaching him. "Well BoCo, how are you enjoying your trial on the Island of Sodor up to this point?"

"It's a lot to take in all at once to be honest, sir," BoCo admitted. "But I did talk with a diesel named Rusty for a couple minutes. I wasn't, aware that they made engines that small."

The Fat Controller merely let out a jovial laugh in response and gazed at him. "Never you worry about that. For the time being, I want you to learn the Ffarquhar Branch Line and become better acquainted with the engines there. Should I have an engine show you the way there?"

"That should be fine, sir. I don't want to end up getting lost after all." The Fat Controller nodded in approval.

"Very well then, I'll have Mavis meet you here." An hour later, another horn was heard as Mavis approached Crovan's Gate. "Mavis, I want you to show BoCo here around the Ffarquhar Branch Line."

"Of course, sir. Hey, shall we go now then?" Mavis asked while glancing at BoCo. After hearing his response, the two engines soon set off for the Ffarquhar Branch Line. But when they were halfway to their destination, both of them had to stop for some fuel since neither of them wanted to end up becoming stranded on the Mainline.

It took another hour and a half, but they eventually arrived at Knapford, which was where the Ffarquhar Branch Line started. "Well, here we are. But it'll take a while to become familiar with everything on this branch line." Setting off again, Mavis began showing BoCo around the Ffarquhar Branch Line. Several hours and a couple refueling stops later, Anopha Quarry could be seen up ahead. But by this point, the sun was now starting to go down.

"I wasn't aware that it was so late now," BoCo said as he looked around Anopha Quarry.

"Hmm, you'll get used to it eventually. But why not stay the night in the sheds here?" Mavis offered. "There's more than enough room for it after all." Smiling, BoCo was reversed into the sheds by his driver. Their drivers then left for the night once BoCo and Mavis were both shut down.

One by one, the engines on the Island of Sodor all fell asleep for the night. All except for the engines at Tidmouth Sheds, who consisted of Henry, Gordon, James, Donald and Douglas.

"Disgraceful!" Gordon hissed.

"Disgusting!" James snapped.

"Despicable!" Henry declared. James soon looked at Henry and Gordon.

"Listen you two, the Fat Controller has made a mistake by allowing another one of their kind on the island after what happened in 1957 and that visiting diesel during Stepney's visit. As for what made him purchase Daisy and Mavis, I don't get it. That new diesel on trial has no place on this island, so I say we should make this quite clear to the Fat Controller."

"And what are you suggesting we do, James. Go on strike again? Need I remind you that he gladly locked the three of us in the sheds as punishment while Thomas, Edward and Percy managed all the goods and passengers during that temporary period," Gordon retorted.

"I doubt that any of us have ideas right now, so just sleep on it and maybe something will come to us by morning," Henry told the two of them. Henry, Gordon and James fell asleep after a couple minutes. But Donald and Douglas stayed up a while longer before falling asleep, reliving memories of their own harrowing journey to Sodor in an attempt to avoid being scrapped.