We set out on the James River, March 25, 1865, aboard the paddle steamboat the River Queen. President Lincoln is on his way to General Grant's headquarters at City Point, Virginia, and he's decided he won't return to Washington until he's witnessed, or perhaps even orchestrated, the end of the Civil War. Now, it turns out, more than a century and a half later, historians are still searching for that end. Was it April 9th, at Appomattox, as conventional...