There are numerous series written about former CIA agents that are not included in this collection but the Mystic Rebel is because of its unique nature. It is the only series I have found that has the agent working for, or at least taking suggestions from, the Dalai Lama.
Bart Lasker is an agent for the CIA. He isn't officially on their payroll and he would not really consider himself one but they provided most of his income and occupied most of his time so for all intents and purposes, he was an agent.
Lasker had been a pilot in the U.S. Air Force and had enjoyed it a lot. He would have stayed in as a career but a series of small infractions and arguments had added up and he knew he would not be allowed to re-up. Choosing to get his release in Singapore, he was certain that the need for private pilots he'd heard of would get him plenty of work. Several weeks went by with no bites and too much time to drink. That is when Donnely approached him with a job offer. Donnely would provide the plane, Lasker would do the flying, and a package would be couriered to New Delhi.
The job went without a hitch and was followed by more and more such jobs and Lasker earned a lot of money, enough to put a down payment on his own Vicker P3 Mail plane. Making the payments, though, meant that Donnely really owned him. And that is when he learned that Donnely had definite plans for him. Donnely does not ever state that he is CIA, the cover blurbs on the books indicate it.
As the series begins, Lasker is sent to fly a shipment into forbidden Tibet and while there to note activities by both the Chinese overlords and the Tibetan rebels. He gets shot down and survives only with the help of a mountain tribe who is at first distrustful but then gradually more open.
Shortly thereafter, Lasker discovers his presence and his awakening to the plight of the Tibetans is not a coincidence - he is the fulfillment of an ancient legend and he is given special powers to help him fight oppressors as well as the followers of the Dark One, an ancient evil bent on returning to this world.
After the first adventure when Lasker is back in his old haunts and wondering what he would do with the knowledge he had gained, he was approached by the Dalai Lama who said he had a use for such a man.