By his own account, Cadillac Jack McGriff, 6 feet 5 inches of Texas manhood without his boots or Stetson, 35 years old and twice divorced, is a natural scout and a natural womanizer. Having done a stint as a bulldogger on the rodeo circuit, he retired to roam the country in his big pearl-colored Caddy with peach velour interior. He now spends his days scouting—exploring back roads for antiques and collectibles, buying and selling what strikes his fancy, "too curious, too restless, too much in love with the treasure hunt" to specialize.

The double conceit of scouting and that fancy vehicle allows Larry McMurtry … the peculiar luxury of a rambling, often incoherent, frequently entertaining tale….

But every time Mr. McMurtry threatens to get into something like substantive plot or character development, Jack jumps into that dad-blamed car and drives off somewhere. The cruising is endless and serves only to connect...