A Script for Danger

A film is being made in River Heights, and there's sabotage on the set in this tenth book of the Nancy Drew Diaries, a fresh approach to a classic mystery series.
Nancy's old friend and former paralegal to Carson Drew, Alex Burgess, is making a movie, and it's filming in River Heights! On the first day of shooting, Alex invites Nancy, Bess, and George on set for a behind-the-scenes peek at how a movie is made. George is excited for a closer look at the cameras and special effects, and Bess is mostly around to get a glimpse of the film's leading man: handsome actor Brian Newsome!
But right before the camera starts rolling there's an explosion in the catering area. Turns out someone put firecrackers in the coffeemaker. Not too long after that, Brian's costume is found streaked with blood. And threatening notes show up scrawled on the scripts: SHUT IT DOWN OR YOU'LL BE SORRY.
Can Nancy track down the set saboteur before the film's dangerous final scene? Or will the entire production go up in flames first?