British police have now arrested 24 people in a plot to blow up 10 planes bound for the US, causing what one official called "mass murder on an unimaginable scale." On CNN, Secretary of Homeland Security Michael Chertoff agreed it was the biggest threat to this country since September 11. The discovery, which has American airports on "high" alert, includes LAX, where five airlines operate 20 daily non-stops to and from London-Heathrow. There's no evidence that LA-bound planes were targeted, but Mayor Villaraigosa calls it "a target of opportunity" and confirms a "clear and rapid response" today at all levels of government, indicating that that the city was prepared. New security measures instituted today will mean long lines and require early arrivals. No liquids will be allowed in carry-on baggage because they might be components of explosives. We get details of how the latest reported conspiracy will disrupt travel plans at the height of vacation season.