There are many ways to describe an angel—the inexplicable subatomic output of a black hole called Angelmass—but there is only one way to describe its effect. Those who stay in contact with an angel start doing what's morally right, even if they never have before. The Empyrean, a group of ex-Earth colonies near Angelmass, believes it has found nothing less than an elemental particle of good. Over the past two decades, it's equipped all its leaders with angels, ushering in a new age of peace and a new economy based on angel harvesting.

The nearby Pax empire doesn't like it. Aggressive and acquisitive, the Pax—driven by a shadow government of bean-counting Adjutors—calls the angels an alien invasion by mind control and moves to take over the Empyrean for its own good. The broad Pax strategy includes secreting Kosta, a young scientist hurriedly trained in espionage, inside the Empyrean's Angelmass Institute. Kosta's mission is to learn as much as possible about the virtue-spewing black hole while an impossibly massive Pax starship locates the chink in the Empyrean's defenses.

En route, Kosta encounters a teen-age grifter named Chandris, who's hoping for the impossible score: stealing an angel to sell on the black market. Quickly established among his fellow scientists, Kosta stumbles across surprising evidence that Angelmass's output is increasing. His findings don't fit the plans of High Senator Forsythe, a maverick who fears the angels' mollifying influence. Forsythe quashes Kosta's research, forcing him to gather data the only way he can—aboard an angel-hunting ship bound for Angelmass. To their mutual dismay, it's the same ship onto which Chandris had already wormed her way.

Their lives twisted together by fast-moving events, Kosta, Chandris and Forsythe must face the true nature of Angelmass, the spectacular Pax invasion and their own mutual distrust.

A philosophical page-turner

Some of the best science fiction comes from the marriage of a simple, inspired idea and a dedication to extrapolating the social, political, economic, military and (yes) scientific effects this idea would have on people who look a lot like us. Niven and Pournelle, for example, have excelled at this in novels like The Mote in God's Eye. The trick seems to be developing archetypical, empty-vessel characters that refract their societies like prisms, without reducing these characters to ciphers.

Angelmass achieves this goal. Through Chandris, Kosta, Forsythe and others, a carefully imagined societal interplay is uncovered through characters that are complex, engrossing and unpredictable.

Kosta, the tenderfoot scientist-spy, is our ambassador to Angelmass. He's been subjected to both Empyrean and Pax propaganda, and now he's stumbling on new data about Angelmass that skewers all existing theory. He never knows what to believe, which propels the suspense about the novel's central mysteries: What is Angelmass, and what do angels really do? Chandris—smart, scared and scrappy—is an intriguing tide pool of emotions and vulnerabilities, and if her mentally disturbed ex is little more than a transparent plot device, that's not her fault, is it?

Forsythe represents the undercurrent of doubt that accompanies all such spiraling movements: the dissent that dare not speak its name. As Forsythe acts unilaterally to defend an Empyrean ruled by angel-complacent colleagues, he shivers with the loneliness of his position and, like Kosta, with the fear that he might be the one that's got it all wrong. The neglect that non-angel elements of the economy have suffered is symbolized by the deteriorating city of Magasca rather than thoroughly explored.

Angelmass could have been the pretext for a much heavier investigation of good and evil, but Zahn has spun a richly layered page-turner spiced with interesting people, sharp turns and a few meaningful glares.