Another mystery-this one close to home!Abbi Wallace habitually records animal noises, and her mother recently gave her a special microphone that can detect high-pitched bat noises and make them audible to humans. But one October evening, the old elevator at the Maine castle where they live is broken. Abbi, who now uses a wheelchair due to spinal muscular atrophy, can't get up the stairs anymore, so she has to instruct her friends Lydia and Daniel Herrera on how to set up the equipment via walkie-talkies. Later, the sound app on Abbi's phone makes a screeching noise even more shrill than a whistling teakettle! Abbi's mother teases that it's probably the ghost of the castle's builder. Lydia becomes frightened at the possibility. To appease Lydia's fears, Abbi uses a tablet with a camera to digitally supervise her friends through an auditory search of the house for the source of the noise. Abbi has a hunch, and the next day, they call a park ranger for help. This second series installment gets more personal, addressing Abbi's needs and wants as a wheelchair user, and when Abbi voices her frustration about her lack of access to parts of the castle, her mom is quick to find solutions. The mystery itself is more straightforward but more immediately significant as it takes place in Abbi's home, with great use of technology throughout as the kids-and readers-learn more about bats. Burgett's illustrations continue to delight. Abbi and her mother present white, while Lydia and Daniel are cued Latine.Pleasing entertainment laced with insightful lessons. (bat facts) (Mystery. 7-11)