In a famous passage at the beginning of ‘A Case of Identity’, Holmes imagines surveying the inner workings of the households of London from the air:

Besides the clear reference to Shakespeare's Hamlet, this passage alludes to a French reinterpretation of an ancient myth which, as Anthea Trodd and others have shown, fascinated Victorian writers: Alain-René Lesage's Le Diable boiteux (1707) takes the figure of Asmodeus from Hebrew myth and turns him into a satirical figure who leads ‘a favoured human companion on a roof-top excursion of Madrid, and lifts the roofs of the houses to expose the secret crimes habitually being enacted beneath’. Dickens, Thackeray and George Eliot all invoked Asmodeus in their writing, with the most celebrated instance coming in Dombey and Son (1848):

Dickens's concern is to expose the want and suffering of which Dombey is blithely ignorant, while Conan Doyle suggests that what lies beneath our rooftops is a more diverse set of mysteries and complications. But in both cases, Asmodeus's power is a metaphor for the revelation of domestic secrets and this, for Doyle as for his Victorian predecessors, was a major theme. The plots of the Holmes stories, like those of the Victorian novels with which Doyle was deeply familiar, turn again and again on a suppressed family history.