I enjoyed this story. To be clear, I do not finish stories that I do not enjoy, why bother. Suspension of disbelief is not more required here then it is in a story when a wife comes home to find her husband fucking their fourteen year old daughter and strips off and joins them instead of cutting his nuts off.
So back in time they go, sent from a corporation for "scientific research." Or not.
The woman doctor, her companion (female)/aide/mechanic/lover, and of course the former military special operator. Needless to say, you cannot go back in time without a trusty fifty caliber sniper rifle with a night scope...I mean who would do that? In fact that 50 cal was my one real problem with the story, our hero keeps firing it off hand, and sometimes from the back of a horse, which he manages to stay on. My guess is he never fired a fifty cal sniper rifle.
There is much mystery in this, we do not really know when or where they are. The people they encounter are hunter-gatherers; they have not yet discovered agriculture. Normally that would put the story about ten thousand years in the past. And chauvinist that I am, I was assuming that wherever they were, they were in what is now the United States. But they had horses. Horses got here when the Europeans got here, so wherever they are, they ain't here...or, parallel time line. I am assuming we will find out when the story is finished and it is almost finished.
There is a lot of sex happening and most of it is off screen and not much of it is described in any really erotic way. If you are looking for a stroke story, read one marked stroke story.
There are a lot of descriptions of how our timeline intersects with a more primitive society. Since that society, in this story, doesn't seem to be violent I am not sure who the primitives actually are.
The Blind Man spends time describing how he and those he gathers about him survive and then thrive. Introducing some technology (which is of course magic, thank you Arthur C. Clark) takes up less space than one would imagine, or at least less space than i had anticipated. He does take up a lot of space describing what he sees and how he and the rest adapt to their situation. I found this interesting and creative. He does not go into all the detail that Roust does on the prison planet, he does however do into enough detail to keep those parts of the story interesting.
It is relatively well edited and proofread; as a grad student I know all to well just how difficult it can be to make a long story/paper mistake free. Dr. P. at my school will mark off points for a misplaced coma in a footnote. As she said, she's not Willy Wonka and does not sugar coat excrement. I love that line. It's how I teach. It was also my answer when I was asked if I grade on a curve. But back to "What Lies Beyond."
If you like time travel to significantly less technically advanced cultures, then this is a most enjoyable story.