Lights, Camera, Action -- Geronimo Stilton goes Hollywood as he tires to solve a new mystery surrounding the production of Block Cheddar 4! Geronimo Stilton is getting into the movies when he is invited by an old filmmaker friend, director E.J. Sprocket, to visit the set of Block Cheddar 4, starring Jack Vole. Convinced that this could make for an interesting article he brings Thea, Benjamin, and Pandora along. But soon, they discover that it's not all glitz and glamour as strange happenings have been plaguing production causing the film to go off course. Will Geronimo's acting career be over before it starts? Is there a MOLE on the set? As E.J. would say, “That's show business for ya, baby!”