However Long the Day is the tale of two strangers—Niall Donovan, a poor immigrant from Ireland, and Frederick Philips, a rich ne'er-do-well from New York's Upper East Side—who discover they look so similar they could be twins. Frederick, desperate to avoid a lecture from his father, bribes Niall to switch places for the evening. Niall finds there's more to the story than Frederick let on, and is dragged through the turbulence created by World War I, the Spanish Flu, and social upheaval, and into the corrupt belly of Manhattan on the cusp of Prohibition.

As Niall and Frederick hurtle through the next twenty-four hours, will either get what they bargained for?