The Galaxy Primes

From the back cover of the Ace first edition: "The ship was called the Pleiades, and it was Earth's first starship. It could travel instantaneously to literally anywhere in the universe - but that was the trouble with it. For the was absolutely no way of predicting where in the infinities of space it would reappear when it winked out of the Solar System, and no way of knowing how to return. Its crew was two men and two women, each a Psionic Prime with mind-powers unparalleled in Earth's history. The tale of how they pitted their powers against an entire universe is one of daring adventure on the galactic scale such as could only have been written by science fiction's all-time great, Edward E. Smith."