The British busting up of a terrorist plot - one that was within days of blowing up as many as 10 U.S. airliners somewhere over the Atlantic - demonstrates once again that we have two enemies in the War on Terror: terrorists and our own complacency.

Just shy of five years since 9/11, the sad reality is that the "Long War" against terrorism sure looks to be far from over. In fact, the British investigation is still ongoing, which means we're not out of the woods on even this plot yet.

But this latest terrorist conspiracy, described by British authorities as an act to commit "mass murder on an unimaginable scale," screams at us to pay attention to some new - and enduring - lessons as we continue fighting terrorism both at home and abroad.

First: While the London plot bears all the hallmarks of a classic al Qaeda operation, U.S. and U.K. officials say the 20-plus arrestees are British citizens of Pakistani origin - that is, "homegrown," like last year's 7/7 London subway bombers.

Meaning? Al Qaeda - which seemed to be a terrorist group on 9/11 - is now a global terrorist movement. Osama bin Laden is much more of a worldwide inspiration to his disciples than an active commander directing operations.

Second: Our first line of defense is good, actionable intelligence. That definitely includes the most vigorous collection and analysis of foreign - and domestic - terrorist-related information that our laws and values will permit.

The foiling of this plot clearly shows the importance - and wisdom - behind well-crafted intelligence programs like the NSA's Terrorist Surveillance Program and the tracking of terrorist-related international financial transactions, among others.

Third: International intelligence and law-enforcement cooperation is a force multiplier in fighting terrorism. The U.S./U.K. collaboration in foiling this terrorist operation is well known. But early reports indicate that the London terror cell(s) had ties into Pakistan as well. (No surprise there.) It appears that Pakistan's Interservices Intelligence (ISI) may have pitched in to help scuttle this plot; still, concerns about ISI's loyalties remain.

Fourth: Al Qaeda and its acolytes continue to evolve their operational techniques, including becoming increasingly sophisticated in their evil handiwork.

This plot is a good example: These terrorists reportedly planned to smuggle undetectable components such as "liquid explosive ingredients and detonating devices disguised as beverages, electronic devices, and other common objects" aboard the targeted aircraft.

That looks similar to a mid-'90s al Qaeda operation code-named Bojinka hatched out of the Philippines to bring down 10 or so U.S. planes over the Pacific. But these new techniques were meant to evade post-9/11 security.

You can't help but wonder whether any airport screeners - in Britain or anywhere else - would have been able to prevent the execution of this sophisticated plot if it hadn't been interrupted before it went into action.

Bottom line? Complacency about terrorism is deadly. We're still squarely in the terrorists' cross-hairs. Hopes and wishes that terrorism is something that happens overseas, or was limited to the horrors of 9/11, are clearly unfounded.

And we have to be more imaginative and innovative in our defense than the terrorists are on offense. For instance, we need new security procedures, education and technologies that can detect and prevent "copycat" terrorist attacks, especially overseas.

Of course, being on the offense against the terrorists - using all the "hard" and "soft" instruments of national power, and in cooperation with international partners - is our best defense, whether it's in Iraq, Afghanistan, the Horn of Africa or southern Lebanon.

This may not be the last of the terror plots meant to occur on or near the fifth anniversary of 9/11 by al Qaeda or al Qaeda-wannabes. It certainly won't be the last terrorist scheme we will face in our lifetimes.

Yesterday saw a clear win in the War on Terror, probably preventing the death of as many as 4,000 trans-Atlantic air travelers. But victory in fighting terror often isn't final - and complacency can kill.

Peter Brookes, a senior fellow at The Heritage Foundation, is the author of "A Devil's Triangle: Terrorism, WMD and Rogue States."