It has been hired by Happily Ever After, Inc., a wedding consulting service at which Nancy's friend Bess Marvin works.
In the end, the saboteur turns out to be Grace Sayer, the previous owner of the house.
She had lost the house due to debts and intended to regain it by frightening all its inhabitants.
A message is sent to the fourth bride warning her to stop the marriage before it is too late.
Nancy discovers that Rafe, the security guard, is an ex-boyfriend of the fourth bride and is the one who sent the letter.