"Saboteurs on the River" by Mildred A. Wirt is a fictional mystery novel written in the early 1940s. The story centers around the energetic young protagonist, Penny Parker, and her best friend Louise Sidell, as they become embroiled in an adventure involving sabotage near their hometown's river. The narrative unfolds with a mix of humor and suspense, showcasing Penny's investigative spirit as she seeks to solve the mystery surrounding recent sabotage incidents, including the dynamiting of a local bridge. The opening of the book introduces readers to Penny and Louise embarking on a late-night sailing adventure. The girls' fun quickly turns into chaos when they capsize their boat while reaching for a mysterious bottle in the water, ultimately leading to a series of thrilling events. Following their rescue, they learn about a saboteur who has blown up a bridge, bringing a wave of excitement and intrigue into their investigation. Amidst the friendship, a peculiar character known as Old Noah, who claims to prepare for an impending flood, emerges, adding an additional layer to the mystery Penny is determined to unravel. (This is an automatically generated summary.)