Commercial artist Si Morley is recruited into a secretive government project testing whether self-hypnosis, combined with a recreated slice of 1880s Manhattan, can send someone back in time. He has his own reason to go: his girlfriend has found letters from 1882 hinting at a fire and a suicide tied to a mysterious associate of President Cleveland, and Si is assigned to observe events as they unfold. Working from an apartment in the largely unchanged Dakota building, Si's early attempts succeed, dropping him into a realized nineteenth-century New York whose mystery deepens the more he sees. Jack Finney's time-travel novel doubles as a love letter to old New York.
Summary by Loreful, from public sources