"Vincent and his dad are on a bus in Mexico, headed to his late mom's village of Nagual, when he hears a loud animal roar! Oddly, no one else seems to have heard it. Looking out the window, he is surprised to see a girl running alongside the bus; he's even more amazed when she turns into a jaguar! And then he sees a sinister sight: a woman with a cadaverous-looking donkey's head whose glowing red eyes burn as if on fire! Even in a different country, there's another monster mystery to solve. The boy monster fighter has never met his mother's side of the family, but he knows his maternal grandfather Federico blames his dad for taking Luz away. Despite the tension, Vincent is excited to meet his granddad, Aunt Marina and cousins Pedro and Lupe, who looks suspiciously like the girl he saw running beside the bus! Vincent soon learns that Lupe, like many others in the village, is a nagual, someone born with the magical ability to transform into an animal. His cousins tell him the Donkey Lady hasn't been seen in years, so why has she come back now? They are also alarmed when Vincent tells them that his girlfriend Zulema, a witch owl, is coming to visit. Their grandfather hates witch owls! All too soon, this sixth novel in Garza's bilingual Monster Fighter Mystery series culminates in a convergence of supernatural beings--witch owls, the demonic Donkey Lady, curanderos and naguals--all fighting in a life-or-death battle!"