The Changeling concerns an esteemed New York pianist/composer named John Russell (George C. Scott) who accepts a lectureship position in Seattle for solitude and restoration following the deaths of his wife and daughter in a roadside accident. Claire Norman (Trish  Van Devere), a volunteer at the local Historical Preservation Society, moves him into a massive old Victorian-Gothic mansion located outside the city that hasn't had anyone living in it in at least twelve years. Russell soon discovers that the house isn't as uninhabited as he thought, as things begin to occur (banging noises, bathroom water taps, a boy's image is glimpsed within the water) though it could also be his grief-fueled imagination. He's told that the house has a history and doesn't want people living in it.

Later, Russell senses the house wants to tell him something. He discovers a locked secret room that resembles a nursery, containing a rusty wheelchair and an antique music box that plays a song he'd been composing since he entered the house. Claire tries to help, digging into the sordid history of the house, including a revealing seance that leads them to make contact with the spirit within who provides more clues to the 70-year-old mystery that must be solved to find peace.