The Monster in the Attic by Quincy Hansen
Maren sat on the edge of the couch with her eyes pinned to the front door, refusing to so much as blink. Her friend Wren sat beside her, equally still, equally quiet. From somewhere upstairs, a soft thump traveled down through the ceiling like a question. Maren felt her heart kick into a faster rhythm and silently begged it to settle; the two kids they had been hired to watch had been asleep for an hour at least, and she was nearly certain she had locked every door and window before sundown. She hoped, almost prayed, that Wren could not see her hands trembling against her knees. Wren stared up at the dark staircase with an expression Maren could not read. The thump came again, twice this time, evenly spaced, and Maren could no longer pretend she did not know what the right word was. Footsteps, she thought. The right word was footsteps.