Art Keller, a blond, blue-eyed CIA agent, sits inside a decrepit building deep inside al-Qaeda territory, staring at his computer screen. He is forbidden by his Pakistani minders from venturing out into the badlands of Waziristan to help to find and kill the world’s most wanted man.

He is sick and exhausted, and suffering from food poisoning. Back home in the US his father is dying of cancer. The plumbing is basic, the heat intense — the generator has failed again. He pores over cables looking for any scrap of information — an intercepted phone call, an aerial photograph — that might finally end the hunt for Osama bin Laden…

“One of the things the agency has done is to bring back these old hands,” Mr Keller says, men who despite their age “are willing to spend many months in conditions most people would say is akin to prison”. Mr Keller, who has retired from the CIA and is now a freelance writer in New Mexico, adds: “The divorce rate is very high — it’s through the roof. Yet it’s part of the allure that keeps on driving them back. A lot of the time you are just sitting there reading stuff but you are also in the right area, it’s the big show — you are at retirement age but are you really going to sign up for the bowling league?”…

Mr Keller believes bin Laden moves from village to village in Waziristan. He communicates perhaps just once a month, and by courier. He never uses a telephone. Mr Keller believes that bin Laden arrives in each village with a small group of bodyguards, when he will sit and talk to the local tribal leader. A large bribe is paid.