It's time to dust off your memory of Greystone Secrets: The Strangers (2019) because this sequel picks up right where it left off. Though Haddix peppers in enough reminders to jog most readers' memories, those new to the series should definitely start at the beginning. The three Greystone siblings (Chess, Emma, and Finn) and their friend Natalie are desperately trying to crack the code that will help them save their mothers from the hostile parallel world where they are imprisoned. A breakthrough lands the kids in Other-Natalie's house the parallel world mirrors much of the protagonists' world, including the people living in it on the eve of a large political soiree, leaving them little time to stage a rescue and figure out whom in this world they can trust. Readers will have a ball scurrying through the secret passageways as the tense caper unfolds, but Haddix also gives plenty of page time to the kids' inner musings. Thus readers are ensured a rich mystery-adventure that will activate their brains and sense of empathy.--Julia Smith Copyright 2020 Booklist

Four kids rush to rescue their families from the clutches of a tyrannical government in an alternate dimension. In series opener The Strangers (2019), siblings Finn, Emma, and Chess escaped the parallel world into which their mother disappeared, but they still failed to reunite their family. During their desperate flight from danger, the Greystone siblings' friend Natalie Mayhew lost her mother there, too. Their only path between worlds, a lever stuck to the wall of the Greystones' basement, broke. Now all four kids must work together to reopen the tunnel to a dangerous dystopia and decipher the secret code that Kate Greystone left for her children to solve. This sequel never slows in pace, thrusting the characters into new, treacherous mysteries. In this sequel, Haddix explores themes of honesty and love as the children compare their experiences to those in the alternate universe. Natalie struggles with her relationship with her parents, who are divorced in one world and married in the other. The third-person perspective shifts chapter by chapter among the characters; the Greystone kids present white, and Natalie is biracial, with a Mexican mom and white dad. At times, the setting is logistically disorienting, such as the maze of secret passages and the multilevel glass-roofed event space somehow hidden behind a curtain in the basement of Natalie's house in the alternate world. A perilous, high-action plot--with a cliffhanger. (Science fiction. 8-12) Copyright (c) Kirkus Reviews, used with permission.