This first episode looks at how the West became involved in abductions, secret prisons and even torture, and how the intelligence services successfully disrupt major terrorist plots.
This second episode looks at how, with harsh interrogation techniques increasingly off-limits, spy agencies have developed a controversial high-tech method of targeting and killing suspected terrorists with pilotless drone aircraft. And Peter Taylor reports from Guantanamo Bay on how governments have been forced to face up to the end game - what to do with the hard core Al Qaeda suspects and whether it is necessary to talk to Al Qaeda.