A major focus of this novel is London itself. Lively foregrounds and personifies the city, describing it as "throb[bing]" and "pulsing" and portraying it as being fueled by the energies of the myriad individuals who inhabit it. This impression of the city's richness and texturedness is in part effected by the frequent cataloguing of the sights, sounds, and smells that bombard Matthew on his daily traversings of the city: the various ethnic restaurants, the cacophony of languages, the pastiche of architectural styles from different eras.

One of Lively's purposes in foregrounding London is to demonstrate the web like quality of the city, that is, the way its inhabitants' lives are inextricably and imperceptibly interconnected. Lively achieves this effect by frequently sliding from a close-up view of Matthew's activities to an aerial perspective, from which we can observe "the city's mysterious intestinal life" and detect the mazelike pattern Matthew creates as his path intersects with the paths of other people. This maze includes not only present inhabitants but the ghosts of past inhabitants as well. Using an unusual technique whereby the main narrative is continually interrupted by narratives about prior inhabitants of the neighborhoods Matthew visits, Lively suggests that echoes of these former lives continue to reverberate and to affect future dwellers. The presence of the past, always a theme in Lively's novels, here thus takes on almost mystical dimensions.

Another major concern of the novel is the paradoxical subjective-objective nature of reality. The title implies, and Lively herself has stated, that the work's main thesis is that London, like any city — and like reality itself — exists only in the mind of the beholder. She utters this idea through Matthew, who remarks to a colleague, "This city is entirely in the mind. It is a construct of the memory and the intellect. Without you and me it hasn't got a chance." What Lively is getting at here is a point she expresses in many of her novels: One's perception of a place is shaped by one's mental cargo, especially by one's knowledge of history and literature; only young children, the primitive, and the completely uneducated can see reality in a raw, anarchic way. In a sense, then, she is asserting the philosophy of solipsism, the theory that the self is the only reality.

But on the other hand, in this novel Lively also suggests that reality has an existence apart from the mind beholding it. An omniscient narrator presents episodes from the past (narrated in the intermittent subnarratives) of which Matthew has no knowledge, thereby indicating that the past has an actual, objective existence. Also, a recurring motif is the vastness of the star-filled night sky, and a number of the scenes are set against this backdrop, with the effect of dwarfing Matthew's concerns and significance. Lively explicitly points to the paradox of reality and the dialectic between mind and object when she describes Matthew Halland as "a person of no great significance, and yet omniscient" and Martin Frobisher, the Elizabethan navigator featured in one of the subnarratives, as "a pinpoint in infinity, and a universe."