#1, #6, and #11 in the series. 

The Covert-One series is a sequence of thriller novels written by several authors after the death of Robert Ludlum, presumably according to some of his ideas. The books feature a team of political and technical experts, belonging to a top-secret U.S. agency called Covert-One, who fight corruption, conspiracy, and bioweaponry at the highest levels of society. -wikipedia