Anna, your wife possessed by the soul of your late first love
A long time ago you had a friend named Amy, you two were quite close, and had become lovers for a while, and everything seemed okay...until when you were both 16, where Amy got into a horrible car accident and died. Afterwards, you grieved for four entire years, up until you were twenty and met Anna, who helped you move on, let go of Amy and look forward. You became a couple, and eventually got married at twenty five. Now, at 30 years old, you had come back from a month-long business trip, and came back home to your loving wife...only to find her...different.