Rendell/Vine's technique of bringing two disturbed characters together at the climax of a suspense novel, seen in The Bridesmaid (1989), has modulated in Gallowglass into an overt comparison between the normal and the disturbed.

The abnormal sexual patterns she has hinted at in several previous novels, like the experimental relationship between two women in The House of Stairs (although both characters claim it is not a lesbian affair), is limited in Gallowglass to the mildly incestuous overtones of Tilly's choice of Joe as lover. Joe seems incapable of any sort of physical passion: He asks plaintively, "However you look at sex, it's not attractive, is it?" Because of these shifts in emphasis, Gallowglass seems both more conventional and less powerful a novel than the earlier Vine books. This novel more closely resembles Rendell's Wexford novels, which conventionally pit normalcy against criminal aberration, occasionally to a degree...