When it was time to leave for London, the students turned in their papers and headed inside Star Train. Alya noticed how tired Marinette was, and to keep her identity as Ladybug as secret, since she was up all night fighting an akuma, Arthur told Alya that his mom kept her up. Alya was a bit shocked to hear Arthur, one, had a mom, and two, she was there, but let it go quickly.
"Arthur, hold on." Miss Bustier stopped him before he entered. "Are you sure you want to go? Shirou might not be happy about you leaving Paris."
"It'll be fine, it's just one day, what harm can come from it?"
Arthur was quite chipper in his response; he smiled to her and entered the train right as Chloe and Sabrina arrived. There was also someone else hiding in the crowd, a man, and his daughter; a girl with purple hair, without a doubt, it was Kaede and Assassin. He walked past them, and sat down next to Tamamo, who used her bow to cover her ears since she couldn't wear her hat on the train. The two kept a close eye on the pair, and as a Caster, Tamamo would be aware if they tried anything faster than him.
When Star Train took off, Assassin immediately ran to the bathroom and Tamamo perked up, she got Arthur's attention before he fell asleep then told him about Assassin. She also pointed to Kaede, who was going through his bag. Nothing suspicious to the other passengers around them, but they knew better, it was the Holy Grail War, and those two were known for their shady business.
Tamamo looked around to find Adrien; he was sitting next to Marinette while she was sleeping on him. There was no way for either her or Arthur to talk to them without causing a scene. The entire train then shook as it reached the underwater rails, both Tamamo and Arthur stood up as they heard someone run along the top of the train. Arthur went to the space between cars and climbed up to the top while Tamamo stayed inside to get Adrien and Marinette's attention.
Assassin met Arthur with daggers by her side. She smiled at him as she greeted him and took off her cloak to reveal her black suit, she was ready to fight him as he changed into his armor.
"Did you hear that?" Sabrina asked Chloe as she got a luggage bag from the compartment.
"Hear what?" Chloe asked back.
"I thought I heard something hit the train."
The train shook again, causing some of the people to drop what they were holding, they all looked up at the ceiling of the train as they heard banging noises from above. It woke up Marinette and she excused herself to head to the bathroom as Adrien ran off as well, leaving Tamamo to go the opposite direction as she went to help Arthur.
Both Ladybug and Chat Noir arrived to investigate and keep morale up among the passengers. Ladybug then focused her attention on Kaede, who got up with his bag over his shoulders, she asked him to stay in his seat, but he pushed her away and continued his way. Chat Noir told her not to pay attention to him, as the people were scared and stayed in their seats as they told the heroes what they heard.
Another banging made the train shake, a dragging of blades was also heard as the top of Star train was forced open. A mist entered the train and knocked out most of the passengers. All except for Ladybug and Chat Noir. Ladybug spun her yo-yo to blow the mist away and went to each of the people still conscious. The entire train shook again, then, something was thrown inside.
"Be careful Ladybug!" Chat Noir warned as Ladybug went over to who was on the ground.
"Run," it was Arthur, who was covered in cuts and brushed. "Hurry!"
"Holy Sword Wielder!" Assassin jumped down with her daggers in hand and clashed blades with Arthur.
"It's the Assassin class servant. Get out of here now!" Arthur stood up and fought Assassin while the superheroes ran to the next car.
"You two again?" Kaede asked as he held a vial in his hands, the entire car was empty as the passengers had escaped from his other vial, which was on the floor broken with a yellow liquid mixed with the glass. "I was expecting a master to show up, not you kids."
"Who are you?" Chat Noir asked.
"Kaede Einzbern, nice to meet you kid. Unfortunately, I have no intention of fighting you."
"Then what are you here for?" Ladybug asked.
"I'm looking for something, it's really none of your business."
"You've threatened everyone on the train! It is our business."
"I thought your business was with the akuma attacks, look, we don't get in your business, so you don't get in ours."
"Like hell we're letting you get away with this!" Chat Noir snapped.
"Fine, if you won't leave me alone, I'll make you." Kaede opened a vial and threw it on the floor, the stench it released was horrible, however, it wasn't enough to stop the superheroes. They were able to breathe through the filter in their weapon, the same when they used it underwater.
Kaede held a vial with a red liquid in it and threw it on the ground, the floor melted, revealing the rails underneath. Star Train was going so fast, that if anyone fell, they would be cut in half by the metal left behind. Kaede waved to the superheroes before he made his escape. Just before Chat Noir went after him, Tamamo was thrown back and nearly fell into the hole if Chat Noir hadn't caught her.
She gestured for Chat Noir to push her back into the car and he did, Ladybug had little time to question her appearance before the train completely stopped. One of the students, Max, quickly ran to the front of the train to see if his mother was okay. She was the operator, and if the train stopped, it meant she was in trouble. Ladybug and Chat Noir followed him to find her passed out on the operator table and a vial on the floor.
With the door leading in melted, it was clear who was culprit, but the question of why he did it was up in the air. Most of the passengers were either in hiding or unconscious, meaning he didn't intend on hurting them.
Max stayed behind to help his mother as the superheroes investigated the train. They were stopped at one car, which was where the servants were fighting in, and decided to go around. Since the train was stopped, there was no danger in going outside to move to the next car. Ladybug looked through the window to see Assassin had both Arthur and Tamamo fighting at their best. It was just a shame their masters weren't around to support them.
The next car was empty, all except for the open bags that laid across the floor. When Ladybug opened the door to the final car, the entire scene went black, an ominous atmosphere had taken over and the air turned cold. Kaede was against the wall, completely out of commission from whatever was in there. Deeper inside, a figure that looked like it was wearing a long black cloak stood and stared at the two.
When Arthur and Tamamo caught up with the superheroes, along with Assassin, the three were dead silent. The look on their faces showed complete terror, Assassin went over to Kaede to wake him up, and the other two pulled the superheroes out of the car. Assassin dragged Kaede out just as the car was consumed and turned to dust, the only thing that survived was a piece of golden metal.
"Daddy! Daddy!" Assassin shook Kaede to get him to wake up.
"What was that?" Chat Noir asked.
"Part of the damn Grail," Kaede said as he sat up with Assassin clinging to his chest.
"The Grail?"
"None of your business, it dropped from the bag it was in and completely went insane." Kaede picked it up while Assassin his behind him. "Shirou better pay me extra for this one, I can't believe he's making me do his dirty work. Come on Jackie, let's go."
"Home!" Assassin jumped up and down as the two headed back to Paris by walking.
"Hold on!" Ladybug yelled, "how are you going to get back?"
"Don't underestimate me, I'll be back home in an hour." Kaede waved it off like it was nothing.
"I hope I never see them again," Tamamo complained.
"You're telling me," Arthur said as he rubbed the back of his head.
"By the way," Tamamo looked back at the destroyed train. "What are we going to do about this?"
"There's no akuma," Ladybug said. "So, I don't think my lucky charm is going to work."
"You mean we have to sit here and wait until help arrives?!" Chat Noir said surprised.
"You can't solve everything with magic ladybugs," Arthur sighed. "Come on Caster, let's go back before our masters find out what happened."
"But my master is-" Tamamo started before Arthur covered her mouth.
"Come on and put your bow back on before people see you. Where's the other bow? The one that covers your tail."
"I lost it."