Gleeson, who previously worked with the director on 2014sFrank,tells EW.

Yes, Dr. Faraday is more than a little bit of an oddball.

But creaking floorboards and incessant dust are far from the Ayres biggest problem.

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Nicole Dove/Focus Features

Hes maneuvering himself through his life carefully because hes aware that theres something inside of him.

As it goes on, you begin to feel the house is sick, the people are sick.

As the doctor, he tries to cure them, and then he gets sick himself.

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Nicole Dove/Focus Features

You ask, Where is this all coming from?

Where this is all coming from forms the mystery at the center of the story.

He wants something that he cant have, says Gleeson.

But even with all the money in the world, he would never be thought of at their level.

He will always be from a working-class background.

He will also be new money, the help.

He just burns with shame of it all, and you dont get rid of that.

You carry that for the rest of your life.

Its like a disease that eats away at you as you realize that youll never get what you want.

What they find in each other feels destined to fail, says Gleeson.

The back-and-forth on whether that relationship is good for them is endlessly interesting.

Ruth did such a beautiful job.

We used to laugh about Caroline between takes.

She would be like, Jesus Christ, why would she do that?

Working with her was wonderful.

You dont know who is behind what is happening, Gleeson says.

You dont know whos to blame for the deterioration of these peoples minds as the film progresses.

Are they doing it to themselves?

Is he to blame?

Is she to blame?

Is the maid to blame?

The energy in the house starts feeding Faraday, and Faraday starts feeding the energy.

The Little Strangers potentially paranormal activity aside, does its star believe in such things?

And I think thats scarier: Your mind only gives you things that are useful.

The Little Strangerstarts haunting theaters Aug. 31.