The museum went completely silent.

Milo stared at Inspector Whiskers.

The cat stared back.

Neither moved.

Poppy slowly raised one finger.

“I have a question.”

Milo whispered, “What?”

“Why does the cat have a human-shaped shadow?”

Inspector Whiskers looked down.

His smile disappeared.

“Oh.”

He quickly stepped into a patch of darkness.

The strange shadow vanished.

Milo pointed at him.

“You knew that would happen!”

The cat sighed.

“I was hoping you wouldn’t notice.”

Poppy folded her arms.

“That’s usually what guilty people say.”

“I am not guilty.”

“Then why does your shadow look like a man?”

“Bad lighting.”

Milo looked at the ceiling.

“There are no lights.”

Inspector Whiskers paused.

“Excellent observation.”

Suddenly—

BOOM!

A loud crash came from the second floor.

The three of them jumped.

Professor Wizzlewick rushed toward the staircase.

“We don’t have much time!”

Milo followed.

“Time for what?”

“Midnight!”

Poppy looked at the giant clock.

It was counting backward.

11:42.

11:41.

11:40.

“But you said midnight was coming,” Milo said.

“It is!”

“Then why are we going backward?”

Professor Wizzlewick looked nervous.

“Because the museum is trying to prevent it.”

“That sounds bad.”

“It is extremely bad.”

They reached the second floor.

The hallway was enormous.

Paintings covered the walls.

But these weren’t ordinary paintings.

Each one showed something that had disappeared.

A lost city.

A vanished ship.

A missing crown.

A forgotten forest.

Even a dinosaur stood inside one painting.

Poppy stared.

“Is that a T-Rex?”

Professor Wizzlewick nodded.

“Missing since 65 million years ago.”

Poppy looked impressed.

“How did you find it?”

“We didn’t.”

“Then why is it here?”

The professor pointed at the painting.

“Because someone remembered it.”

Milo frowned.

“So the museum doesn’t collect things people lose?”

“Not exactly.”

“What does it collect?”

The professor looked at him.

“Things the world has forgotten.”

Milo suddenly remembered the voice.

His grandfather.

Don’t trust the cat.

He looked at Inspector Whiskers.

The cat was staring at a painting.

Milo walked toward him.

“What did my grandfather mean?”

The cat didn’t turn.

“I don’t know.”

“You’re lying.”

“I lie professionally.”

Poppy whispered, “That’s not reassuring.”

Milo grabbed the cat gently.

Inspector Whiskers hissed.

“Put me down!”

“Tell me the truth.”

The cat sighed.

“Your grandfather and I worked together.”

Milo froze.

“You knew him?”

“For seventeen years.”

“Then what happened?”

Inspector Whiskers looked away.

“He disappeared.”

“Why?”

“Because he discovered something.”

“What?”

The cat’s expression became serious.

“The museum isn’t a museum.”

Milo waited.

“Then what is it?”

“A lock.”

Poppy blinked.

“A lock for what?”

The cat looked toward the end of the hallway.

“A door.”

“What door?”

Before he could answer, the hallway shook.

A crack appeared in the floor.

Something blue began glowing underneath it.

Professor Wizzlewick shouted:

“Everyone back!”

The floor exploded.

A cloud of silver dust filled the hallway.

When it cleared, a small golden door stood in the middle of the floor.

There was no wall around it.

No frame.

Just a door.

Poppy crouched beside it.

“That’s weird.”

Milo stared.

“There’s something written on it.”

Four words had been carved into the gold.

WHAT IS LOST RETURNS.

Inspector Whiskers became pale.

“No.”

Milo looked at him.

“What?”

“That door should never have opened.”

Professor Wizzlewick walked closer.

“What does it mean?”

The cat whispered:

“Arthur.”

Milo’s heart jumped.

“My grandfather?”

The door handle turned.

Slowly.

Click.

Milo stepped backward.

The door opened.

Darkness filled the hallway.

Then a man’s voice came from inside.

“Milo.”

Milo stopped breathing.

It was his grandfather.

Exactly as he remembered him.

Warm.

Calm.

Familiar.

“Grandpa?”

Poppy grabbed Milo’s sleeve.

“Don’t go in.”

“But that’s him.”

“No,” Inspector Whiskers said.

Milo looked down.

The cat was trembling.

“You said you didn’t know where he was.”

“I didn’t.”

“Then how do you know that’s not him?”

“Because…”

The cat swallowed.

“…I’ve heard that voice before.”

“Where?”

“From inside the museum.”

The voice came again.

“Milo, come here.”

Milo stared into the darkness.

Then a hand appeared.

Old.

Wrinkled.

Wearing a silver ring.

Milo recognized it.

His grandfather had worn that ring every day.

He took a step forward.

Inspector Whiskers jumped in front of him.

“No!”

Milo stopped.

“Move.”

“No.”

“That’s my grandfather.”

“No, Milo.”

The cat looked terrified.

“That thing has his memories.”

Milo’s eyes narrowed.

“What’s the difference?”

Inspector Whiskers whispered:

“Everything.”

Suddenly, the hand disappeared.

The golden door slammed shut.

BANG!

The hallway went dark.

Then every painting on the wall began moving.

Poppy screamed.

The dinosaur stepped out of its frame.

A pirate climbed out of another.

A woman wearing a crown emerged from a third.

Professor Wizzlewick shouted:

“The memories are escaping!”

Milo stared in disbelief.

The dinosaur roared.

Poppy grabbed a broom.

“What am I supposed to do with this?”

“Fight the dinosaur!”

“Why me?”

“You’re holding the broom!”

Poppy swung it.

The dinosaur bit the broom in half.

She stared at the broken handle.

“That was my favorite broom.”

“You’ve never owned a broom,” Milo said.

“I’ve grown emotionally attached!”

Inspector Whiskers jumped onto the dinosaur’s head.

“HEY!”

The dinosaur shook wildly.

“STOP MOVING!”

The cat flew through the air.

“WHISKERS!”

He landed inside a painting.

The painting showed a snowy mountain.

Only his head appeared above the frame.

“I’m fine!”

Milo grabbed Poppy’s hand.

“Run!”

They raced down the hallway.

Behind them, the museum erupted into chaos.

Lost objects floated through the air.

A thousand-year-old crown chased Professor Wizzlewick.

A pirate chased the dinosaur.

The dinosaur chased everyone.

Milo and Poppy reached a staircase.

Then Milo stopped.

“Wait.”

Poppy nearly crashed into him.

“What?”

Milo pointed upward.

At the top of the staircase was a giant circular window.

Through it, they could see the night sky.

But the Moon was wrong.

It had no reflection.

Instead, a dark shape was floating beside it.

A perfect black circle.

Poppy whispered:

“Is that the missing reflection?”

Milo nodded.

The black circle suddenly moved.

It came toward the museum.

Faster.

Faster.

Then—

CRASH!

The window shattered.

The black circle entered the museum.

Every object became completely still.

The dinosaur froze.

The pirate froze.

Even Inspector Whiskers stopped moving.

The black circle floated above Milo.

Then it opened.

Inside was an eye.

A gigantic silver eye.

Milo couldn’t breathe.

A voice filled the museum.

Not loud.

Not quiet.

Everywhere.

“ARTHUR QUINN’S BLOODLINE HAS RETURNED.”

Poppy grabbed Milo’s arm.

“What does that mean?”

The voice continued.

“THE LOCK CAN NOW BE OPENED.”

Milo looked at Professor Wizzlewick.

The professor was shaking.

“What lock?”

Professor Wizzlewick pointed toward the floor.

“The museum.”

Milo frowned.

“What?”

“The museum itself.”

The floor began glowing.

Golden lines spread across the entire building.

A giant symbol appeared beneath them.

It was the same symbol as Milo’s pocket watch.

Inspector Whiskers slowly walked toward him.

His human-shaped shadow appeared again.

This time, Milo could see its face.

It was an older man.

The same man from his grandfather’s photographs.

Milo stared.

“Who is that?”

The cat looked at the shadow.

Then at Milo.

“My real name…”

He hesitated.

“…was Elias Quinn.”

Milo’s eyes widened.

“Quinn?”

Inspector Whiskers nodded.

“I was your grandfather’s younger brother.”

Poppy’s mouth fell open.

“You’re his uncle?”

“Yes.”

“Why are you a cat?”

Elias sighed.

“Long story.”

Milo stared at him.

“You told me not to trust you.”

“I told you not to trust the cat.”

“You ARE the cat!”

“Exactly.”

The museum began shaking again.

The giant eye above them opened wider.

A terrible voice echoed:

“THE DOOR BELOW IS OPENING.”

Milo looked down.

A staircase appeared beneath his feet.

It descended into darkness.

Professor Wizzlewick whispered:

“The original museum.”

Milo swallowed.

“What’s down there?”

Elias looked at him.

“The thing your grandfather spent twenty years trying to keep locked away.”

Milo took a breath.

“Then let’s find out.”

Poppy raised her broken broom.

“I’m coming too.”

Elias sighed.

“Of course you are.”

They stepped onto the hidden staircase.

One step.

Then another.

Behind them, the museum doors slammed shut.

Above them, the giant silver eye slowly closed.

And from deep beneath the museum came a sound that made Milo’s blood freeze.

A man’s voice.

His grandfather’s voice.

But this time, it wasn’t calling him.

It was laughing.

“You finally came home.”