From Time To Time by Jack Finney

A middle-aged man who once learned to travel back to Gilded Age New York is drawn into the past again, navigating richly rendered turn-of-the-century streets and society as he seeks to reclaim a lost love and to prevent forces that would alter history; the novel mixes time-travel mechanics, romantic longing, and meticulous period detail as he races to protect both personal happiness and the integrity of the past.

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