Art and Marsha Parker finally have a chance to get away for a week from Marsha's medical clinic in the small town of Bearford to visit a plush resort for a honeymoon, a gift from their wealthy benefactor, Charles Drummond. Somehow their adopted sixteen-year-old daughter, Mary Ann Markham, who is also Drummond's granddaughter, and Mary Ann's best friend, Jennifer Martin, manage to convince the old man that Art and Marsha need chaperoning, so the two girls show up at the resort at the end of the first week, ostensibly to notify Art and Marsha that they've been booked for another week but really to investigate a corpse--soon to be two--discovered at the foot of a high waterfall on the resort's property. With their usual lack of good luck, all four get involved with searching for counterfeit fifty-dollar bills. Then Art, Mary Ann, and Jennifer manage to get themselves kidnapped by three thugs while attempting some unauthorized detective work on their own. While Marsha, inspired by the waterfalls at the resort, convinces Drummond to build a trail to an overlook for a waterfall on his property, the search for the counterfeiters goes on. Art, Mary Ann, and Jennifer keep getting themselves in more and more trouble until Art and Mary Ann come up with a brainstorm that finally leads them to the head of the counterfeiting ring and almost to their own deaths.