Bird's-Eye View by J. F. Freedman

Fritz Tullis was a successful professor at the University of Texas until he had an affair with the wrong (as in married) woman. He resigned while on leave of absence and is now living in a somewhat renovated sharecropper's shack on family property in southern Maryland. It's on the edge of a swamp where he fishes, photographs the many birds in the area and enjoys the solitude the place offers while he tries to get his head screwed on right.

One day while photographing the birds, he sees a small plane land across the water on the new neighbor's (James Roach) property. He witnesses a murder and vows to himself not to get involved. Then he learns the neighbor is the wealthy, shady assistant secretary of state. Fritz has been reckless most of his life and, against the advice of his lawyer friend, starts nosing into the life and misdeeds of Roach—to see that justice is done. He's soon in way over his head.