The Wedding Day Mystery is the 136th of the Nancy Drew mystery stories published by Simon and Schuster.
Plot summary 
The plot revolves around the happenings taking place at Heights House,a Victorian mansion on the outskirts of River Heights. It was hired by Happily Ever After, Inc., a wedding consulting service at which Nancy's friend Bess Marvin works. Bess' cousin George and Nancy had agreed to assist Bess in the four weddings which were taking place on that weekend. But then a series of mishaps followed. Someone dressed as a ghost frightened the bride when she saw him/her in her closet. Nancy's car was also tampered with, which nearly killed her. The bride's wedding gifts were also stolen and the wedding dress of the bride of the next wedding was slashed to rags. In the end,the saboteur turned 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. But after she was caught during the third wedding, the problems did not end. A message was sent to the fourth bride warning her to stop the marriage before it was too late. Nancy discovered that Rafe, the security guard was also an ex-boyfriend of the bride, and he himself had sent the letter. Nancy and her friends prevented him from stopping the marriage.