The “Doctors Plot”, as the British are calling it, is a sharp reminder that Islamist bombers are not necessarily recruited from the ranks of the poor and oppressed. In fact, Al Qaeda began as a middle-class movement. Its leader, Osama bin Laden, is the son of one of Saudi Arabia's wealthiest entrepreneurs and a millionaire in his own right. His number two, Ayman Al Zawahiri, is an Egyptian doctor and the son of a doctor. The principal actors in the 9/11 attack on the United States were middle class and educated.

The surprising thing about the doctors who have been arrested in the alleged plot to commit mass murder in London and Glasgow was not their backgrounds but their apparent incompetence. All three of their car bombs failed to explode.

Dr. Asha and his son

The question British experts are now asking is where the suspected plotters were recruited. Although they came from the Middle East to work in Britain's National Health Service, there are indications they may have been radicalized by Islamic fundamentalists in Britain. A Jordanian friend of the Dr. Mohammad Abdelkader Asha, one of the accused, told a newspaper, “When I saw him last year during one of his home visits to Jordan, he seemed influenced by the Islamic ideology in Britain. Even physically he was different. He wore the long beard of Islamist extremists.”

If so, that is bad news for the British security services. It is easier to screen potential immigrants in an effort to keep out potential terrorists than to spot legal immigrants who are recruited while already living in Britain. Except for his beard and the fact that his wife (a lab technician who also works for the National Health Service) wears a headscarf and a long robe, the couple and their infant son lived much like their middle-class neighbors in a pleasant area of Newcastle-under-Lyme. The neighbors described them as “discreet,” “quiet” and “respectable.” Dr. Asha had been a brilliant student at medical school in Jordan, where he received his M.D. in 2004, and seemed headed for a bright future in Britain until he was arrested by police after a high speed car chase on an expressway in northern England. His alleged role in the plot may become clearer as police pursue their investigations, but some British newspapers are already describing him as the mastermind.

Arrest of Dr Bilal Abdullah at Glasgow

What could have turned a promising young doctor into a would-be terrorist? It was clearly not his own situation in life. Bob Ayer, a researcher at the British think-tank Chatham House, points out that “Islamic fundamentalism is not an economic phenomenon. It is ideological and anyone can subscribe to it.” One of Osama bin Laden's leading supporters in Britain, a man I first met in London in the late 1990s, was a highly skilled surgeon in Saudi Arabia before he became a political exile. Dr. Saad Al-Fagih's motivation is religious. He campaigns to rid the Middle East of what he sees as corrupt irreligious governments and believes the world would be a better place if we all converted to his brand of Islam. Dr. Asha presumably shares these same goals, but was allegedly ready to take more extreme action to achieve them.

If there is any lesson to be learned from the dramatic events of the past week, it is that there is no standard profile for Islamist terrorists except their willingness to commit mass murder in the pursuit of extremist religious goals. Skilled intelligence and thorough police work are deterrents, but they are not a sure defense against all such attacks. As the Irish Republican Army used to say in its campaign against British rule in Northern Ireland, “We only have to succeed once – you have to be successful every time.”

It took decades for the I.R.A., whose goals were well defined and not totally unreasonable, to merge its campaign into acceptable political action. No one knows how long the threat of Islamist terrorists will be with us. Their goals are nonnegotiable and they think in terms of eternity.