Jefferson key. Steve Berry. 2011.

Four United States presidents have been assassinated. - in 1865, 1881, 1901 and 1963 - each murder seemingly unrelated. But what if those presidents were all killed for the same reason: a clause in the United States Constitution - a clause that would shock the world?

In the most perilous exploit of his life, former Justice Department operative Cotton Malone must combat themCommonwealth, a treacherous, piratical society first assembled during the American Revolution. Along the way, he must break a secret cipher originally possessed by President Thomas Jefferson and unearth a centuries-old document which could make the Commonwealth unstoppable in its lust for power.