A grandfather shows his girl Laura the hide-out cave, and finds there Diego De la Vega's diary about the Devil's fortress, which was used as a feared political prison. Victoria showed a letter, allegedly from her father Alfonso's cell mate, if true he didn't die in the Mexican revolution but is seriously ill. Diego volunteers to go there to speak to the commandant, actually Zorro comes in his saddle bag after promising Victoria his help. The alcalde orders Mendoza to accompany him on a week's trip to the fortress, he wanted an excuse since years, so they go plead ...