Peter Munro is an agent for the Travelers, a branch of the British Secret Service. At least he had been for three years before the first book of the series. Then a mission gone horribly wrong resulted in his partner being shot on the Greece-Albania border and Munro being captured by the Albanians while trying to get the partner to safety.
Before he was a spy, Munro had owned a fairly successful china business, traveling to Dresden in East Germany to purchase exquisite dinnerware and then shipping it to the West for a tidy profit. The ease with which he was able to come and go brought him to the attention of the Travelers, who specialized in such people, namely people who were already experienced in international commerce and who could, through their lines of work and their connections, move about without attracting attention.
Several months of intense training followed his recruitment and then Munro was not only a businessman, he was a contract agent. He was expected to continue to operate his business but also expand its theater of operations to better give him more places he could go without suspicion.
After his friend was shot and he was captured, Munro spent a grueling eighteen months as a prisoner before a swap was arranged. During that time, he was constantly interrogated. Though, he says, no physical damage was done, the mental torture was enough. Upon his repatriation, he quit the agency as he was definitely tired of the work and, with his cover totally blown, they could have no further use of him.
Surprisingly, though, they still very much do have a use for him, but not as he might expect or desire.