"Ralph Martin's wife Jean was young and beautiful .and frigid. Even so, Ralph stayed faithful. Then one morning on the commuter train to the city his eyes caught the breathlessly lovely redhead across the aisle. Her name was Magda and before long he had met and fallen in love with her. He tried hard to conceal it from Jean, his wife. He even introduced the two girls - and to his great surprise, they became fast friends. He was even more surprised when Jean suggested that Magda occupy one of the rooms in their big, empty house! It wasn't long before Martin realized he had a rival for the affections of the lovely Magda. Jean was passionate again, but not for him. And Magdo was slipping futher into the perfumed trap. ralph Martin knew he must fight for what he wanted, and his battle carried him deep into the bizarre, unnatural world of perverse love."
The One Between is a young blonde named Magda, who commutes daily into Manhattan on the Long Island Railroad. A fellow commuter, a man in a loveless, childless marriage sees her every day on the train and begins to fall in love with her. He eventually talks her into clandestine rendezvouses and ultimately talks his wife into taking her in as a border, when the young girl's mother throws her out of her own house.
The wife, seemingly unable to bear children and with a mothering instinct readily accepts the idea of taking in Magda as a border. What husband and wife don't know is that each is trying to seduce the girl.