Although ostensibly an underworld thriller, the book is also noted as the first of Greene's series of religious novels and deals with Roman Catholic doctrine concerning the nature of sin and the basis of morality. Pinkie and Rose are Catholics (as was Greene), and their beliefs are contrasted with Ida's sentimental sense of right and wrong. Greene is also initiating here the series of moral problems with which his later novels wrestle. In this case he is asking what place has a creature as heartless as Pinkie within God's infinite mercy. Rose had wanted to share in the damnation that Pinkie had earned, but the solution to her dilemma only arises indirectly in her interview in the confessional. There the priest refers her to the example of an unnamed Frenchman who rebelled against the Catholic doctrine of divine judgment and "who decided that if any soul was going to be damned, he would be damned too."[4] This was, in fact, the case of the writer Charles Péguy.[5]
Another aspect of the problem's difficulty is the impossibility of changing an environmentally conditioned character, as suggested in the title of the novel. Primarily, rock is a hard type of confectionery sold at seaside resorts, with the town's name embedded in the centre and elongated down its length, so that it is revealed wherever the stick is broken. At the most obvious level, it stands for the tawdry 1930s seaside town, from a disadvantaged part of which both Pinkie and Rose have emerged. But in terms of the plot it is also the murder weapon ironically chosen to choke Hale. And beyond that again, it is the symbol of unchangeable human nature for the trite and morally neutral Ida.[6] It was against just such seeming inflexibility that Péguy reacted.
The way opposites are handled in the novel adds this further layer of complexity to its meaning. The tourist aspect of Brighton and the gangsterism that takes advantage of it are at odds but depend on each other. The affluent characters coming and going in its luxury hotels and bars contrast with the down-and-out beachcomber, the old woman crouching to say her rosary in an alley, and characters like Pinkie and Rose struggling to escape the slums that bred them. Then there is the irreconcilable difference between the Catholic ideological interpretations of good and evil and Ida's humanistic moral intuition, which goes far beyond a simple contrast of alternatives.[7] The two are mutually exclusive. So, when Ida declares in her argument with Rose in Chapter 7:
"I know the difference between Right and Wrong. They didn't teach you that at school," Rose didn't answer; the woman was quite right: the two words meant nothing to her. Their taste was extinguished by stronger foods - Good and Evil.
This leads to a further paradox on which the novel dwells more than once: that, their common origin apart, Pinkie and Rose are so much opposites that they make a whole.[8] As another interpreter has commented, "Their only possible relation is the paradox of the Catholic novel".[9]
