by Dick Francis. Putnam’s, $13.95. Like most of Mr. Francis’s excellent thrillers, this novel has a firm base in reality—specifically, in the practice of releasing a convicted murderer from prison with the optimistic assumption that incarceration has mended his ways. The murderer, a thoroughly nasty type, has gone to prison through the efforts of Jonathan Derry. Once out, he seeks revenge and runs into Jonathan’s younger brother, William. It is a daring move to construct a thriller with two narrators and a gap of fourteen years bang in the middle, but Mr. Francis brings the trick off. With no discernible change in prose style, he makes the Derry brothers unmistakably different people. Jonathan is wily, wary, and, possibly because he teaches physics at a boys’ school full of “little monsters,” inclined to rush in and take charge. William is cheerfully direct and asks only to be left in peace with his mistress and his horses. Mr. Francis has contrived exciting problems for both of them.