Books like the never war

The Never War is a book in the Pendragon series by D.J. MacHale. In this book, the main character, Robert "Bobby" Pendragon follows the antagonist, Saint Dane, to a territory called First Earth, which is essentially Earth in the year 1937.

Bobby Pendragon and Vo Spader, the Traveler from Cloral, arrive on Veelox a few weeks after the death of Bobby's uncle, Press Tilton, only to figure out from Aja Killian, the Traveler from Veelox, that Saint Dane went to First Earth. They flume there (New York City, 1937) to be greeted by bullets from gangsters that Saint Dane has hired. They then met the First Earth Traveler, who saved them from the gangsters. He is a bell captain at the Manhattan Tower Hotel named Vincent Van Dyke, nicknamed "Gunny". Bobby and Spader become employed as bellhops there, and investigate the ties between First Earth's Turning Point, rival crime godfathers Max Rose and Winn Farrow, and the Nazi party.