This is the second of a series of three adventures, each of which can be read on its own or together as a trilogy. The unusual thing about this trilogy is that each is of a slightly different genre.
The full series is
The Disinherited (Space Opera)
Legacy (Time Travel)
Debt of Ages (Alternate history)
Steve White started out his writing career with the "Starfire" books which he co-authored with David Weber. Both writers then branched out on their own, and both developed enormously as a result: "The Disinherited" was the first published novel which Steve White wrote on his own, and "Legacy" is the sequel. In my opinion these books are not at all bad, but are not in the same league as some of his more recent work.
In "The Disinherited" humans from earth in the mid 20th century were contacted by visitors from another star. The good news is that these visitors, the Raehaniv, are friendly: the bad news is that their home world is about to be attacked by a species called the Korvaasha, who are not.
The Korvaasha turn up in all three books in the trilogy: they have a huge and very powerful empire, are horribly evil, and intend to conquer the entire universe. In the first book, rather than face a re-education camp back home and sitting around waiting for Earth to be discovered and conquered by the Korvaasha, some of Earth's astronauts decide to help take the battle to the Korvaasha - but in the process they become the Disinherited.
"Legacy" starts some 200 years later. Earth is in the middle of a major war with a largish fragment of the former Korvaashi empire, a fragment which is if anything even more evil: the "Realm of Tarzhgul" think the previous Karvaashi Unity was run by "bleeding-heart liberals".
On a fringe world, an survey team from earth runs into, in quick succession, explorers from Raehan who soon become friends, an enemy force of Korvaashi, and then time travellers from the far future. And suddenly they find themselves back in the time of King Arthur ....
Overall this is a fairly good book, worth a read if you like space opera. It also solves one or two of the mysteries left over from "The Disinherited.