Henry has been a resident of Sodor for many a long year, and has worked his hardest for most of it. As a mixed traffic locomotive, he can do most of the work assigned to him, assuming it doesn't exceed his power classification of 5. But as useful as he is, he is something of a serial worrier, as is his driver, Fluttershy.
One morning, Henry arrived at Knapford station, unusually facing the Tidmouth end whilst running light engine from Vicarstown. Sir Toppham Hatt was there to greet him on the platform, whilst his two grandchildren stood behind him.
"Good morning Henry and Fluttershy!" he said. "I'm taking Stephen and Bridget out today on the island." Both children stepped forward. Their faces were covered in red spots, which they kept scratching.
"Don't scratch them," Fluttershy said. "That'll only make them worse! That looks like the time Angel came down with the bunnyflu."
"Is there such a thing as a the bunnyflu?"
"Yes, there is."
"Whatever bunnyflu is, neither Stephen nor Bridget have it," said Sir Toppham Hatt. "They've been stuck in quarantine for a few days as they've got chickenpox."
"What's chickenpox?" Henry asked.
"It's an infectious disease," Fluttershy explained. "You don't need to worry about me, I'm already vaccinated against it."
Henry, however, was now very confused. He didn't quite understand what all that was about, and wondered whether engines could catch chickenpox too. Sir Toppham Hatt's car roared off into the distance and bounced along the country lanes as Henry went to fetch his coaches for the day. That, and use a turntable, as otherwise he'd have to run tender first.
Meanwhile, Thomas was picking up some chickens at Farmer Finney's. They were all loaded in wicker boxes, which were then loaded into open sided vans so the chickens could breathe. Meanwhile, Terence was trying to get moving.
"I thought it would be easy to get the old tractor out!" he said. "But this mud is something else."
"Wait a moment, Ah'll increase the clutch," said Big Mac, and he moved the lever and floared the accelerator. Mud flew from Terence's caterpillar tracks and splattered all over Thomas.
"Hey! Watch where you're throwing all that mud!"
"Sorry!" Terence called. "It's this bloomin' tractor!"
"Ah can help wash Thomas off!" Big Mac called. "He does look a bit of a mess."
"Never mind!" Twilight called. "We need to drop these chickens off soon."
"I can always get a wash later!" Thomas added, and he pulled away.
Henry came to a stop at Wellsworth to meet a train coming in from Brendam, but he couldn't stop thinking about chickenpox. He jumped when Edward clattered in with his coaches.
"Good morning Henry!" called Edward.
Applejack hopped off Edward's footplate and secured him. "Why, Henry, yer lookin' sicker than a mule," she said. "How are ya feelin'?"
"It's terrible!" Henry said. "I saw Sir Toppham Hatt's grandchildren earlier today, and they're all spotty. They have chickenpox!"
"So they've got it too," Applejack sighed. "Apple Bloom's cooped up with it too. Ah wanted ta stay and look after her, but Granny an' Grandpa say they can handle it no problem. Besides, chickenpox ain't a big deal when yer a kid."
"I fear I'm going to get it too!" Henry exclaimed.
"I don't think engines can get chickenpox, or at least I've never seen a case of it," Edward mused. "Oh, and your lamp is still wrong. You're a Class B working, not a Class J."
"611?"
"Not that type of Class J!" Edward replied. "Through mineral or empty wagon train."
As Edward moved off to take on water, Thomas arrived with his delivery. "Hello Henry!" he called.
Henry, however, gasped in horror when he saw the sight. "Spots!" he cried. "And chickens! Chickenpox!" He then began to pull away before the doors could be closed.
"Henry! The signal's still at danger!" Fluttershy called. "And it's before our booked departure time!"
Elsewhere, Derek was busy marshalling some stone trucks at Vicarstown when 'Arry arrived with a load of scrap. "Good afternoon 'Arry!" the bigger diesel smiled.
'Arry smiled mischeviously. Seconds later, he shot forwards, smoke shooting from his exhaust and leaving a cloud all over Derek.
Derek coughed. "Good grief! Your engine is in need of a tune-up!"
Octavia coughed and spluttered. "Must you uncultured oafs pollute the air with your buffoonery?"
"Oops!" Arry laughed. "Sorry, Derek!"
Henry was later puffing along the line when he saw Derek approaching on his way to Brendam Docks. His face and bodywork was covered in soot, and he was coughing as he went along. "I think some of that got stuck in my air intakes."
Henry gasped in horror. "Chickenpox! Derek has chickenpox! It can infect diesels too!" He suddenly lurched forward and sped away into the distance.
Derek blinked in confusion. "Chickenpox? Whatever is he talking about?"
"Engines can't get chickenpox," Octavia sighed. "Is this another of Vinyl's pranks?"
Henry was running so fast in his desperation to get away from Derek that the coaches weren't running well. The passengers were hurled about like peas on a frying pan!
"This is terrible! Worse than a boneshaker!" said one.
"If I had wanted to ride on a bumpy train I'd have gone on Northern Rail!" said another.
Just down the line at Kellsthorpe Road, Gordon had called with the Up Wild Nor' Wester, whilst a careless painter was repainting a telephone box. The painter was so careless, he kicked the paint can all over the track, making it look like a murder had just been committed. Moments later, James rushed through and the paint flew everywhere.
The paint was all over the track. It was all over the sleepers. It was all over the station canopy. It was all over the ballast. It was all over Gordon's face. The only place where there was no paint was the painter or the telephone box.
Gordon looked at him angrily. "Oh, the indignity," he fumed.
"How can Gordon pull the express now?" Rainbow Dash asked. "He looks like somebody through a tomato in his face!"
Just then, Henry slowed down for his stop, and saw Gordon's face covered in red spots. He screamed in terror, and immediately began running in reverse- running wrong line!
"CHICKENPOX! CHICKENPOX!"
Henry ran through a set of junctions as Murdoch ground to a halt, the AWS having halted him in an emergency. "Henry!" he snapped. "What's going on? You're not Auto-Fitted!"
"CHICKENPOX IS EVEN SCARIER THAN RAIN!" Henry cried.
"Even I can hear that through my headphones!" Vinyl commented.
Even further down the line, Edward was taking a special train to Vicarstown when he was suddenly swung off into the loop. "What's going on? We've got priority!"
Then they saw Henry race through the section, going wrong line. "Henry! Yer runnin' Wrong Line!" Applejack shouted. "The signals ain't blocked back against ya!"
Henry began reversing up Gordon's Hill, but Gordon was catching up.
"KEEP AWAY! KEEP AWAY!"
Gordon rolled his eyes. "Whatever is the matter with you today? You're going to cause an accident!"
Fluttershy looked out of the cab (although her visibility was severely restricted by the coaches) and was unable to see if anything was behind them. She slammed the brakes on, but this did little good as the regulator had primed.
Sir Toppham Hatt heard all the noise from a nearby road, so parked his car at the side of the road and got out to see what was going on. He nearly did a double take when Henry sped past going wrong line in reverse! "HENRY!" he boomed. "WHAT ON EARTH ARE YOU DOING?"
At Wellsworth, Fluttershy finally got Henry back under control, and shut off steam. She was not happy. "What were you thinking?" she scolded. "You nearly hurt our passengers!"
Just then, Thomas returned from up the branch. There were no longer any spots on his face.
"Thomas?" Henry asked, confused. "What happened to your spots?"
"Nothing a rag and some water couldn't solve," Twilight smiled. "I washed them off whilst at Brendam."
"And my face," said Gordon, "is covered in red paint spilled by a careless painter who didn't seem to understand the concept of yellow lines on platforms."
Henry suddenly felt very silly. "I thought you had chickenpox," he said, looking at the rails. "I'm sorry for all the confusion I caused. I was genuinely frightened I would get it."
"Engines can't get chickenpox," Fluttershy said, her face now understanding. "Not even chickens get it. It's an airborne disease that isn't usually that serious in children, but it can be in adults. I had it before I moved to Sodor, and I was alright again in a few days."
"Likewise!" Sir Toppham Hatt said. "Sadly, Lady Hatt had it as an adult, which was a bit unpleasant but thankfully not too serious. But disease is no joke, and as such you must always make sure your vaccinations are up to date."
After that day, Henry stopped worrying about chickenpox, and went back to being what he usually is. A really useful engine.
Even if a scare did briefly run that diesels could get measles. After all, Coughs and Sneezles spread Diseasles!