The Brubaker house always smells like other people's dinners. Mara has babysat three-year-old Theo eleven times now. Same rules every time: monitor on, door cracked, bed by eight. It's 9:40 and the living room is dark except for the little green screen. Theo is a small white smudge, asleep on his side. Then the screen hisses with static, and when it clears, the smudge is sitting straight up, facing the camera.

Mara stares at the screen. Theo never sits up like that, stiff and still. She turns the volume up. Through the speaker comes a soft sound. Not crying. It's humming. A slow, tuneless hum she has never heard him make. She gets up to go check on him.

Mara climbs the stairs and eases the door open. Theo is tucked in, breathing slow, fast asleep. No humming. She almost laughs at herself. But as she turns to leave, the humming starts again, soft and clear. It's coming from the closet across the room.

Mara opens the closet. Behind the coats sits an old white baby monitor, the same model as the one downstairs. Its screen glows green and shows the living room couch, where a girl exactly like Mara sits watching a screen. Her heart slams. Someone is watching her too, from in here.

Mara watches the screen and waves her hand. The girl on the couch waves back at the exact same moment. Slowly she understands. She is the reflection now. The real girl is downstairs, and Mara is the thing in the closet that got out eleven visits ago. The humming, she realizes, is her own.