The issue of sacrifice—both knowing and unknowing—appears very early in the novel and takes on many forms as the narrative progresses, for the brutally hardscrabble world of London Below overlays the blander realities of London Above, and those who are unlucky enough to become unwitting denizens of the former soon become acquainted with the grim reality that sacrifices must be made in the struggle for survival. Central protagonists and secondary characters alike are used to illustrate the nuances of this theme, and as Richard and his companions work to unravel the mystery lurking beneath the demise of Door’s family, they all become intimately acquainted with the fact that making sacrifices—or accepting the sacrifices of others—comes at a heavy spiritual cost and leaves an indelible mark upon their psyches.

Throughout the fantastical adventures that characterize the novel, Gaiman sprinkles liberal examples of sacrifice to imply that this dynamic is an integral part of London Below, and even secondary characters have their place in this harsh worldview. For example, when the young rat-worshipper Anaesthesia leads Richard over the bridge to the Floating Market, she is devoured amid the darkness simply because a “toll” is required of those who dare to cross the bridge.