Manhattan's rodent population is being terrorized by a vicious night monster, and Fievel's spending many sleepless nights worrying about his family's safety. In search of a little reassurance, Fievel accompanies his sister, Tanya, to her job at the local newspaper. What he gets instead is an assignment to accompany the fearless reporter Nellie Brie as she delves into the story.
Many frightening misadventures follow, and Fievel's family is placed in peril in the process. With a little help from Tony and Tiger, Fievel and Nellie track down the unexpected villain in the depths of the city's sewer system and, ultimately, put her out of commission.