This book had an interesting premise - but unfortunately couldn't deliver because the focus was spent on fight scenes rather than working on resolving the situation. Which is a real shame.
Anyway, the Endeavour is called to a colony which is attacked by an alien ship. After seemingly disarming the ship an away party is dispatched to learn more. But instead of the empty ship they expect the away team stumble across an unknown species which returned to this planet after being driven off in the distant past to recover the remnants of their host species, who live cloaked in subterranean caves, in order to survive... and who now discovers the Endeavour's crew as a means to gain even more hosts.
When I read about the depiction of this alien species who attaches to the host's neck I immediately thought of Babylon 5 and the parasite in Londo. And even if the Lrondi's motives are basically ones of survival and cooperation, they don't ask, they just take hosts and influence them by either taking over the physical reactions entirely or at least inducing negative feelings when the host doesn't agree with the parasite - and also in the other direction force the hosts to see things their way, to tolerate and accept the collection by inducing good feelings - like a drug, I guess. Granted, their aims beyond collecting hosts are benevolent, they try to advance their host species' knowledge. So it's not that they just use their hosts' bodies... still when push comes to shove and they are forced to choose between their own good and that of their hosts, they'll choose their own. It's not equal partnership, it's just that the hosts are allowed to have some say as long as it fits with the Lrondi's agenda.
More than 2 thirds of this book are spent on thwarting the Lrondi's attempts at collecting the Starfleet personnel. On every other page officers's interal struggle of compassion for their captors and the struggle for freedom is depicted. But actually, I just don't get it. Because even those who could be liberated from the Lrondi still feel compassion, they still liked those parasites. Take Cole for example who still argues for the Lrondi Naqa, who actually still puts Naqa's well-being before Klisiewicz's, Naqa's current host. And I think the real story doesn't end with thwarting the attempt, it starts with the aftermath, getting over the collection for the hosts, essentially being violated, taken against your will and manipulated into feeling compassion for the Lrondi, but also trying to find a way for the Lrondi to survive, be it without hosts (which they are capable of) or with willing partners in an equal relationship.
In short, I feel cheated out of a good, potentially great story about overcoming oppression (even benevolent domination is still oppression) and reaching a mutually agreeable status quo between the Pelopans and the Lrondi. Instead I had to wade through length of repetitive story-telling that held virtually no suspense - because let's be honest, since we haven't heard from the Lrondi before, it's a given that they failed in their attempt to "collect" the galaxy in a large scale.
From a series point of view, I still by far prefer the Endeavour to the Sagittarius, but I really hope the whole series picks up speed because so far, it's been at most average.