This paper focuses on sewer gas, one of the most feared types of bad air in the nineteenth century. Sewer gas cannot be understood apart from the modern city because the fear of it emerged out of the process of creating the modern city: specifically, it was the by-product of the water carriage systems introduced from the late 1850s to flush away the city’s stagnating waste and hence the source of miasmas and diseases like cholera. It is ironic that the resulting sanitary infrastructure – sewers, pipes, plumbing, and bathroom fittings – then became the means by which sewer gas entered the home, along with diphtheria and typhoid. With the increase in the number of households installing modern plumbing, the anxiety about sewer gas increased. It spiked dramatically in 1871 when the Prince of Wales was struck down by typhoid. The two-month saga of his illness, updated daily by every British newspaper, become a detective story of sorts, as the medical journal The Lancet undertook – and published – a sanitary audit of the Prince’s residence to find the source of his infection. The soil pipes and sewers were all minutely inspected. Even the royal water closet was not spared. Following the Prince’s illness, sanitarians began urging wives and mothers to regularly inspect their homes for sewer gas leaks. They used cutaways – slices through houses that revealed drains, soil and vent pipes – to highlight potential sources of gas; directional arrows represented air currents and leaks. But, in mapping the ways in which these flows of water and air linked up formerly discrete fixtures and spaces, cutaways also offered clear evidence that the relationship between bodies, interiors, and the outside world was being profoundly reconfigured by the new infrastructural complexity of the modern city.