The Moonlight Child by KAREN MCQUESTION (e-book)

On a cold January night, Sharon Lemke heads outside to see a lunar eclipse when she notices something odd at the house behind her backyard. Through her neighbor's kitchen window, she sees what appears to be a little girl washing dishes late at night. But the Fleming family doesn't have a child that age, and even if they did, why would she be doing housework at this late hour?

It would be easy for Sharon to just let this go, but when eighteen-year-old Niki, a former foster child, comes to live with Sharon, she notices suspicious activity at the Flemings' house as well. When calling social services doesn't result in swift action, the two decide to investigate on their own.