Mrs. Bunsen stood at the front of the room. She was wearing a white lab coat and safety goggles that made her eyes look huge.

"Chemical reactions," Mrs. Bunsen said. "It is when two substances meet and change. They create energy. They create heat. Sometimes, they create an explosion."

Alex sat at his desk. He was carefully pouring a blue liquid into a clear liquid.

"Precision," Alex whispered. "Drop by drop."

Mark sat next to him. Mark was wearing his safety goggles upside down. He was holding a test tube full of bright green sludge.

"Mrs. Bunsen!" Mark shouted. "My potion is bubbling! I think I created life! I will name him Slimey!"

"Mark," Mrs. Bunsen sighed. "Please do not name the chemical waste. And please do not drink it."

"It smells like apple juice," Mark said, sniffing the tube.

"It is copper chloride," Alex said. "If you drink it, you will turn green and explode."

"Cool," Mark said. "Like the Hulk."

Maya was at the next table. She was mixing her chemicals perfectly. The liquid turned a beautiful shade of pink.

"Reaction complete," Maya said. "The catalyst worked."

"Catalyst," Alex repeated.

He liked that word.

A catalyst was something that made a reaction happen faster. It made things explode without being used up itself.

"That is me," Alex thought. "I am the catalyst."

The bell rang.

"Class dismissed," Mrs. Bunsen said. "And Mark, please wash your hands. You are glowing."

"I am radioactive!" Mark cheered. "I have superpowers!"

Alex packed his bag.

School was over. But the real chemistry test was tonight.

The FA Cup. Fourth Round.

Manchester United. Away.

Old Trafford.

They called it The Theatre of Dreams. But for away teams, it was usually the Theatre of Nightmares.

Alex walked out to the car park.

Milo was waiting.

Milo was dressed as... a Devil.

He was wearing a full red bodysuit with a pointy tail and plastic horns. He was holding a pitchfork made of cardboard.

"THE RED DEVIL!" Milo screamed. "I AM HERE TO SCARE THE OPPOSITION! ALEX! I AM SELLING HOLY WATER! IT BURNS THE DEMONS! IT IS JUST TAP WATER WITH LEMON! BUT IT IS BLESSED BY ME!"

"Milo, you look like a spicy pepper," Alex laughed.

"I AM HOT STUFF!" Milo yelled, poking a bush with his pitchfork.

They drove to Manchester.

The journey was long. Mark fell asleep in the back seat. He was snoring. It sounded like a chemical reaction gone wrong.

They arrived at Old Trafford.

The stadium was huge. It was red brick and history.

Steve, the manager, gathered the team in the dressing room.

"Manchester United," Steve said. "They are back. They have found their rhythm. They have Casemiro in the middle. He is a tank. He stops everything."

He looked at Alex.

"Professor. Casemiro is a neutralizing agent. He stops reactions. Your job is to start them."

"I will be the catalyst," Alex said.

"Good," Steve said. "And watch out for Rashford. He is fast. Not Mark fast. But fast."

"Nobody is Mark fast," Mark said, waking up from a nap on the massage table. "I am the speed of sound."

They walked out of the tunnel.

The noise was loud. Seventy five thousand fans.

The United fans were singing Glory Glory Man United.

Alex looked at the United team.

Bruno Fernandes looked angry. Marcus Rashford looked focused.

And Casemiro.

He looked like a wall. He had a face that said You shall not pass.

The whistle blew.

The game started.

It was a battle.

United played with aggression. They pressed high.

In the fifth minute, Alex got the ball.

He tried to turn.

Casemiro slammed into him.

It felt like being hit by a bus.

Alex fell to the grass.

The referee waved play on.

"Welcome to Old Trafford," Casemiro grunted.

Alex stood up. He checked his ribs. They were still there.

"Okay," Alex thought. "Physical force is high. Resistance is maximum."

The game was stuck in the midfield.

It was a gridlock.

Arsenal tried to pass. United blocked.

United tried to run. Arsenal blocked.

In the thirtieth minute, Rashford got the ball.

He ran at Ben White.

Rashford did a chop. He cut inside.

He shot.

Ramsdale made a save.

The ball bounced out to Bruno Fernandes.

Bruno volleyed it.

It hit the post.

CLANG.

The crowd groaned.

"Wake up!" Steve shouted from the sideline. "Mix it up!"

Alex looked at Mark.

Mark was on the wing. He was waving his arms.

"I AM OPEN!" Mark yelled. "I AM LONELY!"

Alex wanted to pass to him. But Luke Shaw was marking him tight.

Alex needed a reaction.

Forty fifth minute.

Alex got the ball deep.

Casemiro came to tackle him again.

Alex did not try to fight the tank.

He used chemistry.

He passed the ball backward to Saliba.

Casemiro chased the ball. He stepped forward.

This left a space behind him.

Saliba passed it back to Alex.

Alex was now in the space.

He turned.

He saw the pitch.

He saw Mark making a run.

But the angle was bad.

Alex saw Maya in his head. The catalyst makes things happen faster.

Alex did not control the ball.

He hit it first time.

He hit a "Through Ball" that curved around the defense.

It was a risky pass.

But Mark was fast.

Mark ignited the boosters.

He ran past Luke Shaw.

He collected the ball.

He was in the box.

De Gea came out.

Mark did not shoot. He squared it.

Saka was there.

Saka tapped it in.

Goal.

One zero. Arsenal.

The away fans cheered.

"Chemistry!" Alex shouted.

Halftime. One zero.

Steve was happy.

"You moved the tank," Steve said. "You made Casemiro move. Keep doing it. Make him run. Heavy tanks run out of fuel."

Second half.

United came out angry.

They attacked.

Fifty fifth minute.

Bruno Fernandes got the ball. He chipped it over the defense.

Rashford ran onto it.

He smashed it.

Goal.

One one.

The game was tied.

The Theatre of Dreams woke up. The noise was deafening.

"They are loud!" Mark yelled. "Turn down the volume!"

The game became end to end.

Attack. Defense. Attack. Defense.

Seventy minutes. Eighty minutes.

Alex was tired. His legs felt heavy.

Casemiro was still running. The tank had a lot of fuel.

Eighty eighth minute.

Arsenal had a throw in.

Ben White threw it to Alex.

Alex controlled it.

He was surrounded. Casemiro in front. Fred behind.

There was no way out.

Alex looked for a pass.

He saw nothing.

Then he saw a flash of neon green.

It was Mark's boots.

Mark was standing on the halfway line. He was not running. He was tying his shoelace.

"MARK!" Alex screamed.

Mark stood up.

Alex chipped the ball high into the air.

It went over the midfield.

Mark turned around. He saw the ball coming.

"OH!" Mark yelled. "A PRESENT!"

Mark started to run.

The ball landed. Mark controlled it with his chest.

He was alone.

But Varane was catching up. Varane was fast.

Mark looked back.

"You cannot catch the Emperor!" Mark shouted.

Mark ran towards the goal.

He entered the box.

De Gea stayed on his line.

Mark had time to think.

"Don't think," Alex whispered from the other end of the pitch.

Mark did not think.

He did a "Rainbow Flick".

He flicked the ball over his own head. And over the goalkeeper head.

It was crazy. It was disrespectful. It was impossible.

The ball looped over De Gea.

It dropped into the net.

Goal.

Two one. Arsenal.

The stadium went silent.

Mark stood there. He looked surprised.

"I DID A RAINBOW!" Mark screamed. "WHERE IS THE POT OF GOLD?"

Alex ran the length of the pitch. He jumped on Mark.

"You crazy genius!" Alex laughed. "Who does a rainbow flick in the last minute?"

"I wanted to be fancy!" Mark grinned. "I am a fancy scientist!"

The final whistle blew.

Arsenal 2. Manchester United 1.

They were through to the next round.

Alex walked off the pitch.

Casemiro walked past. He looked tired.

"Good battle," Casemiro said. He patted Alex on the back. It felt like being patted by a bear.

"Good game," Alex said.

Milo ran onto the pitch.

He had lost the devil tail. He was now wearing a white lab coat.

"THE CHEMIST!" Milo shouted. "WE FOUND THE FORMULA! ALEX! THE WINNING ELEMENT! I AM SELLING LOVE POTIONS! THEY MAKE YOU FALL IN LOVE WITH ARSENAL! GUARANTEED RESULTS!"

"Milo, that is just red Gatorade," Alex said.

"IT IS THE ELIXIR OF LIFE!" Milo winked.

They walked into the dressing room.

The team was singing.

Alex sat down. He checked his phone.

A text from Maya.

"Reaction successful. You created a volatile compound in the midfield. Mark goal had a probability of 0.01 percent. It was statistically absurd. But effective. Also, Mrs. Bunsen says you left your safety goggles on your desk. Please collect them tomorrow."

Alex smiled.

He looked at Mark.

Mark was wearing his neon green boots on his hands. He was pretending to be a crab.

"I AM A FAST CRAB!" Mark shouted. "PINCH PINCH!"

Alex shook his head.

They were World Champions. They were top of the league. They were in the FA Cup.

But they were still just kids in a science class, mixing chemicals and hoping for an explosion.

"Let's go home, Crab," Alex said.

"Okay Professor," Mark said. "Can we get pizza? I want to test the chemistry of cheese and pepperoni."

"That is a biology experiment, Mark."

"Whatever," Mark said. "It tastes good."

They walked out of Old Trafford.

The Manchester rain was falling.