It was a sunny autumn day on the Island of Sodor. Percy was taking a load of stone to Brendam Docks. He was enjoying himself. He stopped at a signal by the Vicarage Orchard when suddenly, he heard a very loud whistle. It wasn't like any whistle he usually heard.

Percy gasped. "The Invisible Engine! He's back!" Percy looked all around him; he was very excited. "Hullo?! Invisible Engine!"

"Hullo, Percy."

Percy looked again and saw…Trevor the Traction Engine. "Trevor, did you hear that loud whistle?!"

"Did it sound like...this?" Trevor whistled and the sound wailed all around them.

"Yes! it's…Wait a minute. That was you?"

"Yes. Jem Cole found this old whistle and asked me to try it out once he repaired it. Pretty loud, eh? Thomas says it makes me sound like a big railway engine."

Percy could hardly believe it. "But…I thought…If that was you…then…then I didn't see the Invisible Engine after all."

"You mean Merlin?" Trevor asked.

"Yes. I thought that was his whistle. Another engine came along and heard it too."

"Was this engine big and silver with red wheels?"

Percy thought. "I…I think so."

"I think that was Merlin. I'm sorry to disappoint you, Percy."

"Don't worry," Percy sighed. "It's not your fault." At that moment, the signal changed, and he continued on to the Docks.

Percy was disappointed. Later, he met Thomas at Elsbridge Junction.

"Hullo, Percy. What's the matter?" Thomas asked.

"Thomas, I just found out it wasn't the Invisible Engine I heard before," said Percy sadly. "It was only Trevor. I really thought I saw a magical engine who could make himself disappear."

"Oh, I'm sorry, Percy." Thomas sighed. "I tried to tell you Merlin couldn't really do that."

"So, is Merlin really just a big silver engine with red wheels?"

"I'm afraid so."

"Then why does everyone say he can make himself invisible?"

Thomas explained carefully. "He's an experimental engine. His three funnels were supposed to make him hard to see, but it didn't really work. When he wheeshes steam everywhere and shuts his eyes, he thinks no one can see him, but we don't let him know that."

"Oh," sighed Percy.

Thomas wanted to cheer his friend up. "Don't feel bad, Percy. It's true that Merlin can't really make himself invisible, but he is a very good hider. He surprised me more than once. He even surprised Rebecca. I'm sure you would still like him if you got to know him. He's very friendly."

Percy felt a little better. "Thank you, Thomas."

Thomas watched his friend leave. He felt sorry for his friend. "I wish there was something else I could do," he puffed to himself. Then, an idea flew into his funnel.

Some days later, the Fat Controller asked Percy to take some supplies to Vicarstown Station. Percy arrived on time and waited patiently as the workmen unloaded his trucks.

"Hullo!" Percy jumped. There, beside him, was an engine. He was big and silver…with red wheels…and three funnels.

"Oh," said Percy, "are you Merlin?"

"Yes, and you must be Percy. Thomas told me about you, and he said you wanted to see me."

Percy smiled. "I did." Then, he had a thought. "If you don't mind me asking, can you show me how you turn invisible?"

"Of course, I can," Merlin chuckled. "Just watch…INVISABILITY OOOONN!" Percy watched as smoke and steam billowed everywhere. When it cleared, Merlin was gone. Then, Caitlin puffed out of the station…and there was Merlin. He had been hiding behind Caitlins coaches with his eyes closed. He soon opened them again. "Well, what do you think?"

"Wow!" said Percy, "that was great!"

"I wish I could stay and chat," Merlin continued, "but I have to deliver this steel to Bread-ham Docks."

"Do you mean…Brendam Docks?"

"Yes, that's what I said."

"Oh, I have a delivery to collect from there next. Can we go together?"

Merlin chuckled again. "Of course, Percy."

Percy and Merlin talked happily all the way to the Docks. While they were there, they met Thomas and the three engines set off together. On their way back, they saw Trevor who whistled loudly to them. The three engines whistled back, but the loudest whistle of all was Percy's.

At the end of the day, Merlin left for the Mainland once more.

"What do you think of Merlin now, Percy?" Thomas asked.

Percy smiled. "Well, he may not be invisible, but you were right. He is very friendly…and fun. I really like him."

"I think he likes you two, Percy."

Percy didn't feel sad anymore and now, he was even happier to have gained a new friend in Merlin the Experimental Stealth Engine.