The Phantom of the Theatre

Il Fantasma Del Teatro (The Phantom Of The Theatre) is an Italian children's book by Cristina Brambilla in the "Misteri A 4 Zampe" series.

Premise
The first performance of a famous ballet is ready to go on stage, and the public has great expectations. But suddenly a ghost bursts onstage and scares everybody. It will be up to Mystery Inc. to deal with the case, as usual.