A peaceful vacation for six people and a cat on the quiet island of Martha's Vineyard becomes a wild exercise in mystery solving and survival on the waters of Nantucket Sound for newspaper reporter Mitch Mitchell and his best friend, photographer Alan Jeffrey. Mitch's Grandma Goodie has invited them and their wives and Mitch's mother to spend a week with her in an antique Vineyard cottage. Mitch and Al discover that the million-dollar cottage next door has been stolen from its rightful owners by means of a murder and a falsified will. Their efforts to catch the killer and find the victim's genuine last will and testament lead to a kidnapping and a battle between a millionaire's yacht and a bouncing jet ski on the rough sea waters offshore.