Riddles in an online book-finding game put young cipher sleuths Emily and James on the trail of both buried treasure and a vengeful arsonist.
Amid a welter of clues, codes, mysterious fires, literary references, glimpses of San Francisco sites and history, and developing relationships carried over from the 2015 opener, the tale takes a suspenseful course. It builds increasingly following Emily’s discovery that her social sciences teacher, Mr. Quisling, is receiving coded clues to copies of Tom Sawyer that have been hidden around the city. The seeming game takes a sinister turn when someone (introduced to readers as “the Phoenix” in ominous interludes) torches the bookstore in which Emily loves to hang out, nearly killing her—and then an exhilarating one when Emily, who is white, and her Chinese-American best friend, James, decipher a message in a supposedly unbreakable code on a document that once belonged to Mark Twain. Bertman surrounds Emily with a supporting cast that is diverse in age and personality if not so much in race, and though the arsonist is summarily hustled off after a tidy confession, the multistranded plot does wind up to a climactic conflagration, the excavation of a glittering 19th-century trove, and broad hints of sequels to come.
Brisk, bookish good fun for puzzle and code lovers. (historical afterword) (Mystery. 9-13)