LONDON Plotters in Yemen conceal bombs inside office equipment and mail the packaged items air freight to America. Only a tip-off alerts authorities that planes are en route with a deadly cargo.
A European scare erupts when militants from Germany are reported to be plotting attacks from hideouts in Pakistan. Most subsequently turn out to be incompetent fantasists.
Which conspiracy poses the greater threat? The answer may not be that simple.
In the space of one month the West has faced both starkly divergent scenarios, underlining the complexity of the challenge for counter-terrorism agencies seeking to identify threats, assessing their menace and formulate an effective response.
Al Qaeda is desperate to attack the West five years after its last successful strike, using simpler methods than the kind of complex, team-based operations of Sept 11. 2001.
But forging a common response is difficult, for there is no unanimity among Western experts on whether the diverse tactics it is using, and the emergence of inept novices in its ranks, amount to signs of weakness, or of adaptability.
Bruce Hoffman, a counter-terrorism expert and director of Georgetown University's security studies program, sees no evidence that al Qaeda's energies are fading despite punishing drone attacks on its leaders in the Afghan-Pakistan border area.
"I don't think it's either ebbing or necessarily in retreat," said, pointing to the growth of a globally scattered network of like-minded groups in places like Yemen and Somalia.
Al Qaeda's Yemen network, al Qaeda in the Arabian Peninsula (AQAP), is the top suspect in a global security alert triggered by the discovery of explosives on two cargo planes bound for the United States.
Fawaz Gerges, Professor of Middle Eastern Politics and International Relations at the London School of Economics, said AQAP had the same kind of drive, focus and seasoned leadership as an earlier generation of militants who staged al Qaeda's most prominent attacks including 9/11.
"Their clear message is an intense determination to strike any target, use any method to get at the West," he said.
In contrast, veteran researcher Marc Sageman sees al Qaeda's senior generation "fading away" under pressure from drones, now so bereft of experienced lieutenants that it is forced to use hopefuls who come out to Pakistan to volunteer for duty.
He points to the community of militants in Europe that was at the center of a European security scare in early October.
The group of 11 radicals left Germany in March 2009 to fight against the United States and coalition forces in Afghanistan.
A group member held by U.S. troops in Afghanistan in July 2010 revealed details of planned attacks on targets in Europe, possibly involving simultaneous gun raids in European cities.
To date, the group's performance has been unimpressive.
Of the 11, only eight ever made it to Pakistan. Two, including the ringleader, a Frenchman of Algerian origin, Naamen Meziche, are believed to have been killed in a drone attack.
The others are variously detained in Afghanistan, detained in Germany, living at liberty but under surveillance by the authorities in Germany, or have disappeared from view.
"These are very amateurish groups lacking the sophistication, skills and training of the previous generation that we saw at work in 9/11," Gerges said.
OVERWEIGHT, BUT DREAMING OF JIHAD
"This trend of homegrown militants is alarming and given the number of plots, an attack might get though. But we need to be precise about the nature of the threats: Can al Qaeda carry out spectacular earth-shaking operations any more? No, it can't."
The plot, reportedly hatched in militant hideouts in Pakistan's North Waziristan region, did not appear to have gone beyond brainstorming, security experts say, although there may be other strands of this conspiracy that continue to unfold.
"They lived in a dreamland, dreaming of jihad," a European intelligence source said of the group.
"They traveled to Pakistan with pink-tinted sunglasses, so to speak, looking at a wonderful world. When they arrived in Waziristan they met reality. They had to travel about the mountains, and two of the guys were overweight. It was very strenuous. There were no showers, no meat on the table."
The group's lack of toughness and guile are typical of other radicals who headed to Pakistan from Europe, experts say.
But there is no room for complacency, for when novices rub shoulders with seasoned veterans, they can learn deadly skills.
There have been reports that some of the Hamburg group met Ilyas Kashmiri, a veteran Pakistani Islamist radical. Another contact for European militants is Adnan al-Shukrijumah, an experienced Saudi-born Guyanese al Qaeda operative.
And there are unconfirmed reports that Saif al-Adel, an experienced former al Qaeda security chief, has resurfaced in northwest Pakistan after years of house arrest in Iran.
(Editing by Myra MacDonald)