This is the story of a love that really does span the ages.
The first two parts of this book are actually abridged versions of a pair of Edgar Rice Burroughs novels (that is why he is listed as a co-author). They tell the story of Victoria Custer, your average resident of the early 20th century. She likes candy, her favorite color is pink, and she is very interested in hats and barrettes. She is also deathly afraid of earthquakes, and she is very troubled by dreams and visions of a handsome young man whose name, she learns, is Nu.
A millenia ago, Nu was part of a tribe living in an earthquake-prone part of Africa. It was a time when death could come anywhere and anytime, whether from a snake bite, or being devoured by a large, carnivorous beast. Nu is very interested in taking Nat-ul as his mate. Her "price" is the head of Oo, a very large lion who has caused their group many problems in the past. While off on his solo hunt, an earthquake knocks out Nu, and seals him in a cave, for 100,000 years. Another earthquake opens his cave, and he awakens in the 1920's. For Nu, it's a very boring place, except for meeting Victoria, who is there on a vacation. She could be Nat-ul's identical twin sister. The attraction is immediate, and mutual.
The third part (the part written by Gill) takes Victoria from the family farm in Nebraska to the Yucatan Peninsula, in Mexico. By now, she has embraced her inner cave woman (Nat-ul is now a part of her), and she is planning to visit the Mayan ruins at Chichen Itza. Her brother, Barney, goes with her, knowing that Vic is quite prepared to go by herself. While there, Vic has many adventures, including helping to release several young children from being sold into slavery, killing a jaguar single-handedly, and falling into an underground river, which leads to her almost being devoured by a hideous flying beast. Of course, Vic has a bigger reason for her trip than simply becoming an adventure addict.
I really enjoyed this book. Gill does a very credible continuation of the story of Victoria/Nat-ul. Nearly anything written by ERB will have good writing, and lots of action; so does the third part. This is very much worth the reader's time.