Wolf Rilla writes about lower case characters and lower keyed situations you might not notice -- to begin with. Like Melrose, 45, the butt of everyone's jokes who decides to become the captain of his fate by stealing someone else's 100,000 pounds. Money makes the man of him he never was and he starts all over in Mexico to be followed there by ""Escotland"" Yard's Smith who chaperones him everywhere and before long they quite like each other. This is Graham Greene country -- a comparison not made lightly -- not only in its physical landscape but in its moral uncertainties and subtler shadings (""Anglo-Saxon"" vs. an older uncivilized civilization). Not dispensable -- a literate, terminally exciting novel.