McEwan's book, The Comfort of Strangers, is all the more disturbing, because it leaves many questions without definitive answers. This paper explores one of questions that why Colin, but not Mary is killed. In terms of four characters, Robert in particular is analyzed by psychoanalysis and their relationships, especially relationship between Colin and Mary based on family systems theory, and it can be concluded that the Colin's death is not contingent but inescapable.