Donald and Douglas the Scottish Twins have lived on the Island of Sodor for many years; they enjoy working on the Fat Controller's Railway, but sometimes, they long for Scotland, their old home. "It's a place filled with beautiful landscapes," they say, "and there are many stories and mysteries there too."

Percy remembers the day, not long ago, when a chimney and one of the buildings at the old Quarry Mine near Maithwaite disappeared underground. The Twins had said that it was the legendary Naughty Gnomes. They were only joking of course, but Percy didn't know that, and the engines later found out that the old buildings had only collapsed into some empty mine shafts. Percy was very grateful.

One day, the Fat Controller called the Twins to Brendam Docks; he had exciting news for them. "Lord Callan's Castle is finally reopening; there is to be a grand celebration tomorrow. Donald and Douglas, I need you to take the banners, bunting and bagpipes to the Castle. Harvey, you must load them straight away."

"Yes, Sir," chuffed Harvey. The Twins were excited; Lord Callan was from Scotland like they were and visiting his Castle would be like going home again.

Soon, Harvey had finished loading the trucks. Then, Percy puffed in and saw the Twins' exciting delivery. "Where are you going?"

"Lord Callan's Castle," Donald proudly announced.

"By Castle Loch," Harvey added.

Percy's smile disappeared. "I'm glad I'm not going to Castle Loch," he wheeshed nervously.

"Scared the Monster might get ya!" teased Douglas.

"He might!" said Donald.

The Twins puffed out of the Docks. "Silly Percy," chuckled Douglas, "believing in the Castle Loch Monster."

"And you don't?" asked Donald.

"O' course not, that's just an old story."

"But some visitors to the Loch say they've seen the Monster."

Douglas was getting cross. "Come now, Donal', clearly, those visitors were only seein' things. There's no Monster!"

Now, Donald was upset. "There is too!"

"There is not!"

"Is too!"

"Is not!"

"Is too!"

"Stop bickering, you two," grumbled their Drivers, "tomorrow's going to be a very special day, and we have an important job to do. Now, let's enjoy ourselves."

Lord Callan's Castle is in Misty Valley on Toby's Old Line and it's next to a large lake known as Black Loch. The Castle Loch, as some people call it, is said to be very mysterious and some say that it is home to a big scary monster. Every so often, black shapes have been seen moving around in the water before disappearing…but most people believe they were just seeing things, especially when it's misty.

Donald and Douglas couldn't stay unhappy for long; it was a beautiful day, and they were determined to get the important goods to the Castle on time. They steamed over hills and through valleys until, at last, they puffed proudly around the Loch toward their destination.

"There it is!" cried Donald.

"We're almost there!" shouted Douglas.

But there was trouble ahead.

Trees had fallen across the line. Donald and Douglas stopped just in time. Then, suddenly, there was a rumble…followed by a loud crash. The brake van had been hit by a landslide and come off the rails.

Luckily, no one was hurt, but now, they were stuck. The Twins were worried. "We'll never get to the Castle now," wheeshed Donald.

"It's a pity we can't take the Causeway," said Donald's Driver.

The Causeway stretched across the whole Loch. The tracks were clear, but there was no way for Donald and Douglas to change lines.

"Maybe the Twins can't use it," said Douglas' Driver, "but someone else can. I'll go up to the Castle and call for help." And he ran as fast as he could along the Causeway and up to the Castle.

The Fat Controller was in his Office trying on his present from Lord Callan. "Splendid outfit, Sir," said the Tailor.

Then, the telephone rang, and the Fat Controller heard the news. "Donald and Douglas trapped by the Loch?" he said. "I'll send help as soon as I can."

The hours passed; it grew dark and cold and still, no help had come. Thick fog rolled in, and Donald and Douglas felt very nervous.

Suddenly…the Twins spotted something strange through the mist; it looked like a dark shadow near the Castle, and it started crossing the Loch. "What's that?!" called Donald.

Douglas didn't want to believe what he was seeing; he thought his eyes were playing tricks on him, but no matter how many times he blinked…the dark shape came closer and closer. "I-I-Is it the Monster?!" he cried.

"F-For sure it is!" answered Donald. The Twins closed their eyes tightly and whistled in fright.

"What's the matter?" laughed Donald's Driver.

"It's come to get us!" quivered Donald.

"It's the Castle Loch Monster!" trembled Douglas.

"It's not," said a voice, "it's us!"

Donald and Douglas opened their eyes…it was Harvey and the Breakdown Crane. They were relieved.

By morning, the lines were clear. Donald and Douglas whistled gleefully and hurried off for the Castle. Lord Callan and his workers were waiting to unload the trucks; they had heard about what happened and were pleased that everyone was alright.

Soon, the Castle was decorated, and the reopening was a great success. Lord Callan was pleased. "Och, a splendid pair of engines."

"And very useful," added the Fat Controller.

"Och, aye," agreed the Twins; they still felt silly for believing such a silly story, but they were very happy that everyone could visit Lord Callan's Castle once again.