Edge of danger / Jack Higgins.

Enhanced descriptions from Syndetics:

"The President was running fast now, in the heavy driving rain of Nantucket, and enjoying every minute of it. It washed the years away, and with the world as it was, he could certainly do with that... And in the reeds, the killers waited.""I always return." For centuries, that had been the Rashid family motto. Over the years, the family's British and Arab ancestries had interwoven to produce a remarkable family of warriors, as at home under the pitiless desert sun as in the streets of London. But it is to neither of these places that the Rashids now direct their rage. It is to the United States, whose president they hold accountable for a series of attacks against their power and their honor. From opposite ends of the world, hints are picked up by Blake Johnson, head of the clandestine White House operation known as The Basement, and his Irish colleague, Sean Dillon, but hints to what? By whom? Frantically, they work to find the answer--and meanwhile the killers wait.And that is only the beginning...Brilliantly suspenseful, Edge of Danger is further proof that in the words of the Associated Press: "When it comes to thriller writers, one name stands well above the crowd -- Jack Higgins."