Halfway up the stairs, the humming on the monitor stops. Then a new sound takes its place: footsteps. Small bare feet on hardwood, moving fast. But Theo's door is still shut, and the steps are coming from behind her, down in the dark hall she just left.
Mara whips around. The hall is empty, but the bathroom door at the end now hangs wide open, light off. The footsteps came from there. On the monitor in her hand, the crib view shows Theo asleep and still. So if Theo is in bed, what just ran across the hall?
Mara backs into Theo's room and locks the door. She'll wait it out right here, with him, until his parents come home. She sits against the bed and watches the door. After a while she glances at the monitor still in her hand. The little green screen shows this exact room, and there are two shapes in the bed now. Not one. She turns to look, and screams.