The book has a lot going for it.
One strong point is to depict the live of slaves in Greek cities and contrast their status with that of the Spartan helots. This is part of the author's thesis to show that, at the time, Sparta had the most advanced political regime and society in Greece whereas other cities were ruled by either aristocracies or tyrants, including Athens.
Another point is to show the political life and internal conflicts that could lead to civil war (stasis) within the various cities. Despite its regime, Sparta could also be subject to this, especially if the two kings chose opposite camps.
A third point is to avoid presenting Sparta as the invincible city, which it was not, and to show the dilemma that Spartan Kings, Ephors and members of the Gerousia (the Council of 28 elders plus the two kings) had to face, and the choice that Sparta made. The alternative was to attack and conquer Tegea and its territory, and perhaps even Argos afterwards, just as Sparta had done with Messenia about a century earlier, or to seek alliance through treaties with its neighbors. Even if victorious, Sparta would have had to spread its limited armed forces (only 6000 full citizen hoplites although its lands, according to Aristotle, were sufficient to have a force five times larger than that) thinly, making it even more vulnerable to attacks and rebellions. Sparta chose to ally itself with Tegea, its northern neighbor. This pact of non-agression was the beginning of the Peloponnesian League of free city-states that Sparta dominated and lead, and which excluded Argos, which remained its arch-enemy.
There are a few little issues, however. Despite the author's research and knowledge of the subject, she sometimes get a bit carried away as when she has one character mentioning Alexandria as a possible destination for slaves to be sold. Alexandria, of course, did not exist in 550 BC and was founded by Alexander the Great more than two centuries later. Another little problem, at times, is that the story, which, of course, has a happy ending, seems a little bit too good to be true and some of the characters feel a little bit caricatured: the hero is very, very nice and the villains are, of course, perfectly awful, whether those in Tegea or the Corinthian chariot owner.
Nevertheless, this was a superb read which I thoroughly enjoyed, started and finished over the week-end. It is well worth four stars, although perhaps not five, given the little issues mentioned above.