Repercussions - Unseen Things, #18

Actions have consequences. You may have done something in the past, or perhaps even on this very day that could alter the course of a whole civilization, or simply change the fate of one individual. The gang soon discovers this as they start checking in on some people and places from their past to find out how things have ended up for them over the course of the past two and a half centuries. Also, when Beth organizes a whole new round of exploration runs, Giles and Savaric find themselves on a sunless world in a dimension filled with energy forms that appear to be the ghosts of intelligent species from a variety of different dimensions.
When they bring in Charles and Richard to help them investigate however, one of the energy forms tries to get at them so aggressively, that Richard decides to capture it and bring it back to the lab in order to see if they can use that energy to restore the entity to its original form. Unfortunately, what they end up bringing back is none other than an old enemy that none of them had ever expected to see again.
Repercussions is book 18 of the Unseen Things series.