It was an unusually humid summer evening on the Island of Sodor, and Percy looked exhausted as he was reversed into his berth at the Ffarquhar engine sheds by his driver. Percy would have gladly rested for the rest of the evening until he had to take the mail train, but Toby arrived a couple seconds later and looked at him. "Don't fall asleep yet Percy, the Fat Controller wants us to head to Tidmouth Sheds." Toby then left, Percy following after him while yawning. When Percy and Toby arrived, Thomas was already there waiting along with Henry, Edward, James, Gordon and Emily. The Fat Controller arrived a couple seconds later and the engines winced at the grinding noises coming from Winston. He then walked over and stood before them.
"I'm glad that all of you are on time for my announcement. To help out with the goods traffic on this railway, I have loaned three diesel engines from the Mainland for a month. I expect all of you to be on your best behavior when they get here. Especially the two of you, Gordon and James." The Fat Controller then got into Winston and drove away, Winston making even more grinding noises that faded after a while.
A couple hours later, James, Toby and Emily had no further jobs for the night. So they settled down to sleep. Meanwhile, Henry was being prepared to take the Flying Kipper. But Edward and Gordon had left for Knapford Station. While Gordon would depart first with a night time express train, Edward would depart 10 minutes later with a passenger train. But Thomas and Percy were busy also, being coupled up to some mail trucks so they could deliver the post.
But near the Vicarstown Bridge, three unfamiliar engines were heading silently towards Sodor. After a couple minutes, a whistle was heard behind them. While the two shunters jumped, the larger diesel snarled viciously as his face contorted in anger. "This blasted railway still keeps those disgusting relics around?" The larger diesel then listened as the whistle sounded much closer than before and waited for an opportunity to strike. Caitlin had been returning from the Mainland with some passengers. But after steaming across the Vicarstown Bridge, Caitlin suddenly felt something slam into her with great force and she was knocked onto her side. After Caitlin was knocked unconscious, the coaches she had been pulling now rested on the tracks in an awkward heap. The diesel chuckled darkly at the accident he had caused and addressed the two engines behind him. "Splatter, Dodge, let us go and rest somewhere for the night. For things have only just begun." And with that, the diesel left as Splatter and Dodge followed after him.
The next morning, Hiro was pulling some trucks to the Mainland and was almost at the Vicarstown Bridge when he saw someone urgently waving a red flag. Hiro's driver then applied the brakes to reduce speed. But after noticing Caitlin derailed up ahead, Hiro knew there was no way he could stop in time. "You two have to get to safety," he told his crew in a firm tone. His driver and fireman then jumped clear a couple seconds before their engine crashed into Caitlin and derailed slightly.
But half an hour later, Connor had to pull a longer than usual passenger train with Spencer and was tired of listening to the A4 complain about everything. But Spencer's driver abruptly applied the brakes. "Connor, apply your brakes now! There's a derailment on the line ahead!" The A4 warned. Gasping, Connor's driver applied the brakes as well as they tried to slow down the passenger train. The combined efforts of both engines managed to stop the passenger train a couple inches from the derailed Caitlin and Hiro. The passengers in the train that Connor and Spencer were pulling grumbled at the less than smooth stop. After a couple minutes, BoCo and Bear arrived with Rocky, Judy and Jerome to take Caitlin and Hiro to the Steamworks for repairs.
At the Steamworks, Arthur and Duck were undergoing routine maintenance checks. Victor was then braked to a stop by his driver as BoCo and Bear arrived while pulling Caitlin and Hiro behind them. "Oh my! What happened to the two of you?" Victor asked in concern while assessing Caitlin's condition.
"I don't know Victor," she replied. "I was crossing the Vicarstown Bridge last night when I was suddenly derailed by something. I don't know what caused me to derail." But a sudden whistle was heard as Connor arrived at the Steamworks with a panicked expression.
"Caitlin! Are you alright? Spencer told me what happened and I got here as quick as I could to see if you were alright."
"Yes, I'm alright Connor. But I'm going to be out of service for a while while I undergo repairs." Caitlin then looked sad as she glanced at her coaches. They had been too badly damaged in the crash to be repaired and would be scrapped instead. "My coaches can't be fixed, so they'll be scrapped." Glancing at them as well, Connor also looked sad as he said goodbye to Caitlin and reversed out of the Steamworks.
The Fat Controller then arrived at the Steamworks and climbed down from Molly's cab to assess the condition of Caitlin and Hiro.
Elsewhere, Splatter and Dodge were in a shed when they noticed who was reversing towards them and gulped. "Fancy running into both of you here," he said in a sinister tone after stopping. "We have much to discuss regarding those loathsome steam engines. But with time, this railway shall tremble at the very mention of Diesel 10." Diesel 10 then grinned as he looked around. But Splatter and Dodge hoped they weren't getting in over their cabs by helping Diesel 10.
At Elsbridge, a lone figure was scowling at anyone who tried getting too close to him. He then began muttering angrily to himself. "Watch your back Burnett, I'll finally get you one of these days for taking Tasha from me. Or my name isn't P.T. Boomer." He then got onto his motorcycle and left, the few people on the platform sighing in relief.
After a while, Diesel 10 left to see what other engines he could attack. As he climbed the slope leading to Ulfstead Castle, Diesel 10 growled at Ryan as the tank engine tried saying hello to him. Reaching the top, he noticed Stephen and Glynn resting at a platform. "Everywhere I go on this blasted railway, I see worn out steam engines that should have been scrapped long ago. Especially two useless relics like you. But I'll change that right now."
With a blast of his horn, Diesel 10 proceeded to accelerate and start swinging his claw at Stephen and Glynn. The two engines tried to escape, but he was too quick for them and grabbed a hold of Stephen's buffer beam before starting to pull at it. Stephen then let out a pained scream as it was ripped from his frame and tossed aside. After ripping off Glynn's buffer beam as well, he noticed Millie approaching. But Diesel 10 dropped Glynn's buffer beam while turning his attention to her. "Stay out of this you foolish steam engine, or I'll be more than glad to dismantle you with my claw, piece by piece." He then left Ulfstead Castle, glaring at Millie.
Later that evening in the Blue Mountain Quarry, Luke was just finishing up with his last train of the day when Millie arrived with a panicked expression. Smiling at her, he was confused when Millie didn't respond. After asking what was wrong, she looked at him. "This big diesel I've never seen before arrived at Ulfstead Castle and attacked Stephen before doing the same to Glynn. I tried to stop him, but he was too powerful and ordered me to stay out of it by threatening to use that claw of his to dismantle me." Luke then gasped in shock as he looked at Millie.