Centuries in the future, humankind, an interstellar hegemony operating under the umbrella of the UN, exists alongside five other advanced alien races. Together they form "Tier Three", bound by a diplomatic and trade accord by which little is certain except distrust and conflict. When the kaygryn launch a suicidal assault against an Ascendancy crusade fleet, the fragile imperial compact is thrown into disarray. The Ascendancy is quick to retaliate by massacring the kaygryn, and with a human colony in the midst of the crisis, the UN launches a series of heavy-handed military interventions which succeed only in embroiling it in a deadly alien war. Four UN officials - a petulant strike commander, an ill-informed mecha pilot, a decapitated intelligence agent and an elite, narcissistic diplomat - unwittingly share reservations about the provenance of the conflict. And when the Ascendancy's crusade fleets - vast naval armadas which have been mysteriously pouring into the next galaxy for centuries - begin to slow down, it soon becomes clear that the very survival of the human race is at stake...