Charisma

World apart - Two tall trees lashed by an invisible hurricane on a calm summer day... a hauntingly beautiful girl who would eerily vanish, then reappear ... a mysterious research station in the hills .... They were all linked, John Maine knew, and his sudden desperate passion for the elusive Susanna drove him to discover what the links were - and just what was going on. Maine paid the price for his obsession - for the hidden researchers had opened the way to an infinity of parallel worlds, worlds in which Maine found himself murderer and victim, fugitive and conspirator ... always fated to love and lose Susanna. Then he found a way to escape with her to the "real" world. But that world was not as it seemed - and neither was Susanna. (from the back cover of the Dell Books first American edition)

Novel is a revision and expansion of the short stories "Susanna, Susanna!" and "The Gateway to Now". [source: Galactic Central Bibliography] Author's wikipedia page used to state that the novel incorporates the story "Susanna, Susanna!" but no longer does so as at 2024-12-01