Into the Alternate Universe

Other's called their expedition a "wild ghost chase". But for Space Commodore John Grimes and the beautiful Sonya Verrill who had initiated the project, it was strictly scientific research. Their trip along the rim of the galaxy in search of two men - two dead men - was also an investigation of the long-puzzling phenomenon of the Rim Ghosts. They would do this by penetrating into alternate universes. There was only one real problem involved in this study - how to report its results. For once the breakthrough to an alternate world was achieved, there was no known way of getting out... (from the first page of the Ace Books first edition)