Sally Ratmousen, Editor-in-Chief of The Daily Rat and Geronimo Stilton's biggest journalistic rival, mysteriously disappears one afternoon on the way to her car after work. Her ace reporter, Simon Squealer, shows up at Geronimo's door with the troubling news... and reveals that notorious mobster Barry the Moustache is behind her disappearance. Is he telling Geronimo the truth or is this fake news? If it's a hoax just to generate headlines, Geronimo and Sally might be in over their whiskers as they have upset the wrong mobster.

Based on the animated series now streaming on Netflix