Ley lines provide the way to travel the Neolithic pathways between worlds. The visible universe occupies only one dimension of our common reality. There are other dimensions and where these dimensions impinge on one another, lines of intersection form. Humans can move from one dimension to another along those lines.
We find that it is possible to travel into the past and it is possible for someone from the past to travel to this time. Where we readers live is the Home World and all other worlds and histories are in the past. No one can travel to the future of this world as it has not happened yet.
In general I am critical of fantasy but I thoroughly enjoyed this book. The plot and action are well done. The only miss-step was at the very end where a rescue happens "out of the blue," so to speak. This series will continue but we have to wait nearly a year for the next installment.
Thomas Nelson Publishers, 400 pages.