Ross Murdock (from the first book) is now recruiting others to the organization, including cattle farmer amatuer local archaeologist Travis Fox. The two of them along with archaeologist Gordon Ashe travel back to the time of mammoths to seek out the spaceship of the guys who brought time travel to Earth in the first place.
So, you’re a part of this now, whether or no. We can’t afford to let you go, the situation is too critical. So—you’ll be offered a chance to enlist.

Variants

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  1. Galactic Derelict by Andre Norton (World Publishing Co., 1959).
    2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . written by Andre Norton