Although retired from the US Army, Dave Riley is not out of the action as he battles crafty villains and a deadly pestilence in southwestern Africa in this sixth installment of Mayer's absorbing and well-written series (Cut-Out, 1995, etc.). Now a civilian security specialist hired to protect Satellite News Network correspondent Conner Young, the exSpecial Forces warrant officer accompanies his comely charge to Angola, where she's covering a multinational mission to end the civil strife that's racked the onetime Portuguese colony since it gained independence in 1975. After overrunning rebel strongholds and establishing a base camp along the Zairean border, the Green Berets in the UN's vanguard are stopped cold by the outbreak of a virulent plague. Quarantined with Conner and a handful of soldiers who have also been exposed to whatever's in the air, Dave apprehensively follows the unavailing attempts of epidemiologists who have been flown in from the States to deal with the highly contagious disease they refer to as ``Z.'' Released from hot-zone confinement to escort the medical team on a fact-finding mission, he helps determine that man, not nature, has unleashed the lethal virus. With an assist from the National Security Agency, American commanders soon identify the likely culprit as Pieter Van Wyks, head of the syndicate that effectively controls the world's diamond trade. Aware that the avaricious mining magnate has stockpiled vaccine that can reverse the invariably fatal course of Z, the Pentagon details Dave to lead a small band of nothing-left-to-lose troopers in an airborne assault on the cartel's strongly defended headquarters on the Namibian coast. Though on his last legs and facing die-hard adversaries, the old soldier will manage to beat the odds. A ripping good biotech/military thriller that plausibly depicts the high costs (psychological and otherwise) of combating unseen enemies.