Air date: September 24th, 2015 (UK), October 14th, 2015 (US)
One day, Henry arrives at Knapford where he meets the Fat Controller and his grandchildren. The Fat Controller explains that he is taking the children out in Winston for the day as they have both been stuck at home recently with chickenpox. Henry is worried by the spots on the children's faces; what if engines can catch chickenpox?
Meanwhile, at the farm, Thomas is dropping off some chickens while Butch is trying to pull a tractor out of the mud when he gets stuck. Butch revs his engine and his wheels kick a lot mud up which flies all over Thomas. Luckily, Thomas sees the funny side and knows he can have it washed off after delivering the rest of the chickens.
Henry arrives at Wellsworth station, but he cannot stop thinking about chickenpox. Emily arrives and is concerned that Henry seems very nervous. Henry explains that he saw Bridget and Stephen with spots all over their faces and he is worried he will catch chickenpox, too. Emily tries to reassure Henry by telling him that engines cannot get chickenpox. Henry is relieved momentarily, until he sees Thomas coming towards him with mud splattered all over his face, along with his trucks full of chickens. Henry thinks the mud is chickenpox and races away, scared.
At the Sodor Dieselworks, devious Diesel plays a trick on poor old Paxton and blows dirty, black smoke in the gullible diesel's face. Diesel swiftly exits, leaving Paxton coughing in a mist of thick, black smoke.
Shortly, Henry is taking his passenger train along the main line when Paxton, still coughing and spluttering, approaches him in the opposite direction. Henry thinks the black marks all over Paxton's face are the dreaded chickenpox. Henry is so scared that he races away as fast as his wheels can carry him, causing his passengers to bounce around like peas in a frying pan.
Kellsthorpe Road Station is being repainted when the painter knocks over a tin of red paint. The paint falls onto the rails and Connor runs through it, sending the paint flying into Gordon's face. Henry approaches with his passenger train and spots the red specks of paint on Gordon's face. Now, he is sure Gordon has chickenpox and reverses away at high speed. Henry reverses past a confused Paxton and has a very near-miss with James. Henry carries on backwards up Gordon's Hill when he sees Gordon approaching him in front. Henry orders Gordon to keep away, but the confused express engine cannot work out what is wrong with Henry.
The Fat Controller is still enjoying his day out with Winston and his grandchildren when he gets a big surprise. He spots Henry reversing down the main line and gives chase. Henry is finally stopped at Wellsworth. Just then, Thomas puffs in and Henry cannot work out why the tank engine's spots have gone. Thomas explains it was just mud and he has had it washed off. Then, Gordon arrives and explains that he has red paint on his face. Henry confesses that he thought they both had chickenpox and Thomas tells him that engines cannot get chickenpox as the Fat Controller and his grandchildren arrive in Winston. The Fat Controller clarifies the situation by saying that it is usually only children who get chickenpox and even then, they recover very quickly and it is nothing to be afraid of; he even had it when he was young. The Fat Controller then gives a demonstration of his good health and rips his trousers in the process, revealing a red-spotted pair of underwear.
After that, Henry did not worry about chickenpox again and he even stops to say hello to some chickens near the Sodor Dairy. He meets Paxton there and apologises for running away from him the other day. Paxton finds the situation quite amusing and says that steamies cannot get chickenpox and jokes that maybe diesels can get measles. Paxton makes sure he tells Henry that he is only joking, but poor old Henry still seems concerned.
Tropes featured in the episode:
- A Day in the Limelight: For Henry.
- Attack! Attack... Retreat! Retreat!: When Henry reaches Kellsthorpe, he notices Gordon with paint on his face and thinking he got chicken pox, he instantly starts reversing back the way he came.
- Chickenpox Episode: Sir Topham Hatt's grandchildren, Stephen and Bridgett come down with a case of chicken pox. This causes Henry to worry about if engines can get it as well. He freaks out when he sees Thomas, Paxton, and Gordon with spots on their faces, which are revealed to be mud, dust, and paint, respectively. Towards the end of the episode, Sir Topham Hatt informs Henry that only people can catch chicken pox, but most people get it when they're young and get better quickly.
- Comedic Underwear Exposure: The Fat Controller accidentally tears his trousers while showing off how healthy he is. Much to the amusement of the engines and his grandchildren.
- Here We Go Again!: In the end, Henry knows that engines can't catch chicken pox, but Paxton teases him with saying diesels can get measles.
- Freak Out: Henry's reaction toward engines catching chicken pox throughout the episode.
- Roadside Wave: Both Thomas and Gordon end up on the receiving end of one. Thomas gets splashed with mud from Butch when the latter pulls Farmer McColl's tractor out of it, and Gordon gets splashed with paint when Connor runs over the track covered in paint from a fallen paint can.
- Rule of Three: Henry thinks Thomas has chicken pox because of the mud on his face, then Paxton for the dust on his, and finally Gordon with paint on his.
- In addition, Thomas got the mud on his face from Butch getting stuck, Paxton got dirt from Diesel tricking him, and Gordon got paint on his after paint spills on the tracks and Connor speeds through it.
- Screw This, I'm Outta Here: The sight of Gordon with red spots causes Henry to flee back the other way.
- Sick Episode: Stephen and Bridgett come down with a case of chicken pox in this episode.
- Visual Pun: At the beginning, the title appears while the camera is focused on some spotted underwear on a clothesline.
- Why Did It Have to Be Snakes?: Henry begins believing chicken pox is even scarier than rain.