A family has just moved into an old house. Things go missing. Doors close on their own. The youngest child is not scared — they have made a friend. Boo floats beside them at breakfast. Boo helps them find their toys. Boo is the best secret they have ever kept.

One night the parents hear laughter from the attic. They climb the stairs. They push open the door. Boo is there, sheet swaying, holding a board game. The child looks up and says, 'Boo was lonely. I said they could stay.' The parents look at each other. They look at Boo. And then the dad sits down and says, 'Deal me in.'

Boo has been in the library for as long as anyone can remember. They do not speak. They leave notes — in the margins of books, on the desk, under the lamp. The new librarian finds the first one: 'The third shelf from the left. The red spine.' They follow the clue. They find another note. And another. A trail through the stacks.

At the end of the trail is a single book. Inside is a letter. It is from the librarian who worked here fifty years ago. It is addressed to ' whoever finds this.' It says they were not alone. It says the ghost was their best friend. It says to tell Boo that they never forgot. The librarian looks up. Boo is there. And for the first time, Boo's sheet moves in a way that might be a smile.

Three kids are having a sleepover. They have heard the stories about the ghost in the house. They are trying to be brave. At midnight they turn off the lights and say 'Boo' three times. Nothing happens. They laugh. They get ready for bed. Then the closet door creaks open. Boo floats out. The kids scream. Boo freezes. Boo looks at them. Boo looks at the snacks on the floor. Boo points at the snacks. One kid whispers, 'Do you want some?' Boo nods. They sit in a circle. They share the chips. Boo cannot eat, but they like the company. By morning they are all asleep in a pile — and Boo is floating above them like a blanket, keeping watch.

Someone has lost their key. They have turned the house upside down. They are going to be late. They shout in frustration. The air goes cold. Boo appears. Boo points at the couch. The person looks. Nothing. Boo points again. They lift the cushion. The key is there. They stare at Boo. They say thank you. Boo does not move. They say thank you again. Boo floats to the window and taps the glass. Outside, a cat is sitting on the porch. The person realizes: the cat brought the key in. They had not noticed. Boo had. They open the door. The cat comes in. Boo floats over and settles next to the cat. The person leaves for work. When they come back, the cat is asleep on the couch. Boo is floating above it. And the key is on the hook by the door, right where it belongs.

A wedding is being held in a garden. The couple has chosen the spot because it was the bride's grandmother's favorite place. During the vows, the air shimmers. Boo appears at the back of the crowd. No one else seems to see. The bride sees. She stops. She smiles. She mouths the word 'Grandma?' Boo shakes their head — not quite. Boo points at the groom. Then at the bride. Then Boo floats forward and passes through the space between them. For a second the bride feels a cool touch on her cheek. Then Boo is gone. The bride finishes her vows. Later she tells the groom. He says he felt it too. They decide that some guests do not need an invitation.