George Mado is an agent with the British Secret Service.
Mado is described often as a hard-drinking, womanizing, expendable spy, and he does his best to live down to that description. He is also damned good, which makes him annoying to those who need him and don't want him.
Despite his years and his obvious love of hard spirits, there is still something in his eyes and in the way he watches people that seem to attract the ladies, who sense a bit of danger in him, and warns off would-be troublemakers, who sense he would not back down.
He had been an agent for a considerable number of years, enough to have caused his first marriage to go bust and it has alienated him from his son, a man now grown. Then while on a mission in Czechoslovakia he is betrayed by someone at headquarters and he is caught and imprisoned. Though he is exchanged for another spy, Mado is blown and his time with the Service is over. As the series starts, Mado is earning a living travelling the world selling books.
It is not long, though, before his skills are needed and he is brought back into the fold, especially after he discovers the truth of his betrayal and settles matters his own way.
This series was originally referred to as the "Tarnham secret-service thrillers" as they tend to revolve around Elissa Tarnham, wife of a notorious British Intelligence defector to the Soviets. In fact, you will not find mention of Mado in the first book at all. But once he makes his appearance, he stays the focus. Since the Tarnhams play important roles in the books that Mado is in, and because most lists of the series include the first book, I have done the same. It really should be read to give better understanding to the other stories.