Joe Otterson TV ReporterAllison Williams has boarded the upcoming Showtime limited series “Fellow Travelers” alongside Matt Bomer, Variety has learned exclusively.The series was picked up at Showtime back in April with an eight-episode order. It is based on the novel of the same name by Thomas Mallon.The show is described as an epic love story and political thriller, chronicling the volatile romance of two very different men who meet in the shadow of McCarthy-era Washington.