Mrs. Harper stared at the ventilation grate like she had just seen a ghost.

For a few seconds, nobody spoke.

Then Vincent noticed her expression.

“Harper?”

The house manager quickly looked away.

“I’m sorry, Mr. Moretti. I just remembered something.”

“What?”

She hesitated.

And that hesitation told me more than her words would have.

“The ventilation system was replaced about a year and a half ago.”

Vincent frowned.

“By who?”

Mrs. Harper’s hands tightened around the towels.

“I don’t know.”

“You manage this house.”

“Yes, sir.”

“Then how do you not know?”

Her face became pale.

“Because Mr. Moretti, your instructions came directly from the company that installed it. They said you had already approved everything.”

Vincent looked confused.

“I never approved a full replacement.”

The hallway suddenly felt colder.

I looked between them.

The boys had started getting sick eighteen months ago.

The ventilation system had been replaced eighteen months ago.

The timeline was too perfect.

“Who installed it?” I asked.

Vincent looked at me.

“I’ll find out.”

“No.”

My voice made him pause.

“Don’t ask them yet.”

“Why?”

“Because if someone changed something in this house and nobody told you…”

I looked at the vent.

“They might know you’re looking.”

For the first time since I arrived, Vincent Moretti looked genuinely worried.

Not as a billionaire.

Not as a powerful businessman.

As a father.

“Lucas and Leo are inside,” he said quietly.

I nodded.

“Let me meet them.”

He opened the bedroom door.

The room was beautiful.

Too beautiful.

Everything was carefully arranged.

Expensive furniture.

Educational toys.

A perfect view of the gardens.

But the boys sitting by the window didn’t look like children living in a dream mansion.

They looked tired.

Lucas looked up first.

“Are you the new nanny?”

“Yes.”

“Are you going to leave too?”

The question surprised me.

“Why would I leave?”

He shrugged.

“Everyone leaves.”

My heart tightened.

I walked closer.

“I’m Claire.”

“I’m Lucas.”

The boy beside him smiled weakly.

“I’m Leo.”

They looked identical.

But I noticed something immediately.

Lucas rubbed his arm repeatedly.

Leo kept scratching his neck.

Both movements were small.

Almost invisible.

Unless someone was watching.

“What did you do this morning?” I asked.

They looked confused.

“Nothing.”

“Nothing?”

Leo nodded.

“We rested.”

That answer bothered me.

Seven-year-old boys shouldn’t describe their day as resting.

I looked around the room.

Then I noticed something.

The windows were closed.

The air purifier was running.

But the same sweet artificial smell was stronger here.

I walked toward the purifier.

Vincent followed.

“What are you doing?”

“Looking.”

I removed the filter cover.

Inside was a layer of dust.

But not normal dust.

A strange powdery residue covered the filter.

Vincent’s expression changed.

“What is that?”

“I don’t know yet.”

I looked at him.

“But I know one thing.”

“What?”

“The boys’ symptoms are happening inside this house.”

Before he could answer, the bedroom door suddenly opened.

Dr. Harrison Blake stood there.

His expression was angry.

“What exactly are you doing?”

Vincent turned.

“Dr. Blake.”

The doctor looked at the open purifier.

Then at me.

“You have been here less than one day, and you’re already interfering with medical equipment?”

“I’m observing their environment.”

“You’re a nanny.”

“And you’re a doctor who spent eleven months treating children without asking enough questions.”

The room went silent.

Dr. Blake’s face turned red.

“You have no idea what you’re talking about.”

“Maybe.”

I pointed toward the filter.

“But I know those boys got sick after something in this house changed.”

Vincent looked at the doctor.

“Did you know the ventilation system was replaced?”

A strange pause followed.

Only a second.

But it was enough.

Dr. Blake knew something.

“I don’t handle household maintenance.”

Vincent stepped closer.

“Then why did you suddenly look nervous?”

The doctor said nothing.

That was the first crack.

Later that evening, after the boys fell asleep, Vincent asked me to meet him downstairs.

On the table was a file.

“Private investigation reports.”

I opened it.

Inside were records of every person who had access to the house.

Staff.

Contractors.

Doctors.

Then I saw one name.

My hand stopped.

“Vincent…”

He looked at me.

“What?”

I pointed at the page.

“This person.”

His expression changed.

“What about them?”

“They weren’t just involved with the ventilation system.”

I looked at the date.

“They also accessed Isabella’s old belongings after her death.”

Vincent froze.

“My wife?”

I nodded slowly.

The name on the report belonged to someone he trusted completely.

Someone who had been in his house for years.

Someone who had watched his children become weaker.

And when Vincent turned the next page, we found a hidden maintenance order signed by a person who should have had no reason to touch anything inside the mansion.

A person whose name made Vincent whisper:

“No…”

Because the answer hadn’t been outside the house.

It had been living with them the entire time.