That was Now, This is Then (Temporal Displacement II) – Michael Z. Williamson

In the sequel to A Long Time Until Now, a new displacement occurs, with a neolithic youth appearing in modern day Afghanistan. The same team as before is contacted for a new mission, but not all are keen to go. A pair of scientists are added, much to the dismay of the future humans, who would rather not see too much technology transfer as this could lead to timeline disruption.

The characters are well fleshed out, and there author uses the setting to delve into issues of post-traumatic stress, separation, obligations of marriage, and other things common in deployments. The conflict in the book is not about an external enemy, but rather about the challenges faced by individuals. Much of the book has to do with the strictures and traditions of organisations, and it helps that Mr. Williamson can make discussions on logistics and camp setup interesting reading.