Navarro is kidnapped by Lenz, and Hartman tracks them to an old castle in the Austrian Alps.
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It is learned that Sigma has grown from a simple attempt to plunder the Nazi treasury and stabilize the industrial and financial state of the world in the wake of the war, to a political and financial machine which controls as many as 75% of the world's leading companies, and has enough covert political clout to directly influence the outcome of the likes of Presidential elections.
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Meanwhile, United States Department of Justice Agent Anna Navarro is recruited by a secretive group within the DoJ to investigate the deaths of a list of influential men around the world who have been dying mysteriously.
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The Sigma Protocol is the last novel written completely by Robert Ludlum, and was published posthumously.
Transmission Control Protocol | File Transfer Protocol | Session Initiation Protocol | User Datagram Protocol | Sigma Chi | BitTorrent (protocol) | Kyoto Protocol | Internet Protocol | Sigma Xi | Sigma Alpha Epsilon | Post Office Protocol | Delta Sigma Theta | Program and System Information Protocol | Simple Network Management Protocol | Internet Message Access Protocol | Network File System (protocol) | Hypertext Transfer Protocol | Lightweight Directory Access Protocol | Secure Real-time Transport Protocol | Real-time Transport Protocol | Phi Beta Sigma | Simple Mail Transfer Protocol | Sigma Corporation | Sigma Alpha Mu | Montreal Protocol | Communications protocol | Wireless Application Protocol | SSH File Transfer Protocol | Sigma Phi Epsilon | Sigma |