Summer was approaching on the Island of Sodor. One morning, the Fat Controller arrived at Tidmouth Sheds looking excited. "The Circus will be coming to celebrate the beginning of summer," he said. "It will arrive at Vicarstown next week."

The engines whistled excitedly. "How exciting," said Nia. "I've never seen a Circus before."

"What fun," agreed Rebecca. "The children will love it."

"Also," the Fat Controller continued, "Hank has broken down and gone to the Steamworks, so I am borrowing an engine from the Mainland to do his work."

When the Fat Controller left, the engines got ready to leave too. "I wonder what this engine will be like," said Emily.

"I hope it's Mitchell," Percy replied. "It would be nice to see him again."

Thomas had heard about Mitchell. "If he does come, I'd like to meet him."

"I hope this engine doesn't get to pull the Circus," sniffed James. "One of us should have that chance, especially me."

"Pah," huffed Gordon, "you helped carry the Circus twice already."

"Percy and I had our chance last time too," added Thomas. "It's only fair that someone else does it."

Later, Henry was in Vicarstown Yard when an engine he had never seen before puffed in with some trucks. It had shiny black paint and looked very powerful. "Hullo," said Henry, "are you the engine that's come to help out?"

"That's right. I'm Shamus. Pleased to meet you."

"Right on time," said the Yard Manager. "Now Henry, the Fat Controller wants you to take Shamus with you on your next train so he can learn the line."

Shamus enjoyed working with Henry and Murdoch and soon made friends with them and the other engines. When he heard about the Circus, he was excited too.

Next week came, but the Fat Controller had some news. "There's trouble on the Mainland," he explained. "The engine pulling the Circus has broken down and all the other engines are very busy."

"So the Circus isn't coming?" Percy cut in.

"It will, but it will be delayed. Luckily, the train stopped near a harbour, so arrangements are being made for the Circus to arrive at Brendam Docks."

It took a long time to sort out the confusion and everyone waited anxiously for the Circus to arrive, but when the day came, there was another problem. Salty and Porter were helping to unload the Circus, but all the other engines were very busy. More goods were travelling between Sodor and the Mainland than ever before, and holidaymakers packed the station platforms and docksides.

The Ringmaster was worried. "Worse and worse," he groaned. "We're late enough as it is, and we can't block the sidings."

"I'm afraid there's nothing else we can do," sighed the Dock Manager.

Suddenly, they heard a loud bellowing whistle and Shamus steamed into the Docks with another heavy goods train. "What about that engine?" asked the Ringmaster.

"We can ask."

They quickly explained the situation to Shamus and his Crew. "But we still have more trucks to collect," replied his Driver.

"Where are they going?" asked the Dock Master.

"I'm due to take them to the Mainland on my journey home today before coming back," said Shamus.

The Dock Master checked his delivery list. "Shamus, we need you to pull the Circus. It will take up more space than your next delivery and we mustn't keep the Ringmaster and his performers waiting any longer."

Shamus wasn't sure. "…Alright," he said at last, "I'll do it, but I should warn you, I've never pulled passengers before."

"Oh, don't worry about us," replied the Ringmaster. "Just do your best."

Shamus backed up to the Circus and when everyone was ready, he gave a great heave. The train was heavy, but he slowly managed to pull away.

"Go it, me hearty!" called Salty.

"You can do it, Shamus," cried Porter. Shamus huffed and puffed along the line. It was hard work, but he wouldn't stop.

Finally, tired but triumphant, Shamus reached the Whispering Woods Halt. The performers all said 'thank you,' his Driver and Fireman were pleased, and the Ringmaster was very grateful. "Thank you, Shamus," he said. "You helped to save my Circus."

The Fat Controller was impressed too. "Well done," he boomed.

"I was happy to help," Shamus panted, "but I hope my Superintendent won't be too cross with me."

The Fat Controller smiled. "Don't worry about that, Shamus. You did the right thing and now, you deserve a rest." And Shamus puffed into the sidings and had a long, long drink."

Everyone was happy for Shamus, and he continued to work hard and by the time Murdoch came back, it was time for the Circus to leave. The Fat Controller came to see him…and so did the Ringmaster. "Welcome back, Murdoch and thank you for all your help, Shamus. You have proven yourself to be Really Useful Engine."

"Thank you, Sir."

"And now, I have a surprise for you." He paused impressively. "The Ringmaster and I have spoken with your Superintendent about your work, and we all agree that deserve a more exciting job."

"Shamus," said the Ringmaster, "how would you like to become our very own Circus Engine?"

Shamus could hardly believe it. "Me, Sir?!"

"Yes, we ran into a lot of trouble this last fortnight and we believe it would help everyone if we had our own engines."

Shamus felt happier than he had ever been. "It would be an honour, Sir."

"Hurray for Shamus!" called Rosie and everyone cheered.

Later, Shamus waited at Vicarstown Station for his line to clear. A large crowd had gathered to see him off. "Goodbye, everyone," he called. "I do hope I can come back again."

"I'm sure you will," replied Henry, "and we'll be waiting."

At last, the signal dropped and with a chorus of cheers and whistles, Shamus the Circus Engine set off back to the Mainland.