The Number of the Beast by Robert A Heinlein

Softcover. Condition: Good. 1982. Random House.

When two male and two female supremely sensual, unspeakably cerebral humans find themselves under attack from aliens who want their awesome quantum breakthrough, they take to the skies -- and zoom into the cosmos on a rocket roller coaster ride of adventure and danger, ecstasy and peril.

Second book in The World as Myth series.