One day, after Horace “Ace” Adler wishes for two extra minutes to finish his sixth-grade math final, he feels a sudden blast of freezing air and the classroom briefly becomes a deep-blue, starlit space. When normalcy resumes, the clock has rewound two minutes. The realization that he can time-travel leads Ace to embark on a series of quests. During his expeditions, he encounters a ghostly man wearing white who whisks him away to a giant floating clock with a wild-swinging pendulum that regulates time across the universe. It turns out that a crucial piece of the pendulum is missing; if it’s not found, the man says, the world will end, and it’s up to Ace, with his time-hopping skills, to save it. Before discovering his power, Ace had problems in his own life: His mom died five years earlier, his dad works two jobs (often leaving Ace to fend for himself), and the house where they moved a few years ago feels nothing like home. Now, the future of the planet rests on his shoulders as well. Ace confides in his smart best friend, Alexis, and it’s a race against time as the duo starts decoding clues. They involve unusual items and events that will fuel kids’ imaginations, including a watch belonging to Ace’s father that’s been hidden away; a copy of Madeleine L’Engle’s A Wrinkle in Time (1962), which was an unexpected birthday gift from Ace’s late mother; bizarre connections between the man in white and historic earthquakes; and an enlightening encounter with Christiaan Huygens, the Dutch astronomer who invented the pendulum clock. While the friends’ findings sometimes seem overly convenient, such as a report on natural disasters that’s assigned on the last week of school, and the twists leading to the surprising conclusion may strike some readers as slightly dizzying, the appealing mix of fantasy and reality, related in zippy prose, makes for an entertaining read.