In the transient space of New York City's subway, we share moments with strangers that range from mundane copresence to serendipitous connection to violent conflict. With the rise of Covid-19 in early 2020, as the city’s social stratification seemed to become mapped onto the subway, the social norms that dictate the boundary between public and private behavior shifted. Between the Lines is the culmination of ethnographic fieldwork I conducted on the New York City subway system in the summer of 2021. It also draws from my experiences growing up in New York and riding the subway on a daily basis. This ethnography weaves together first-person stories based on my fieldnotes, the words of my interlocutors, social theory, and analysis to shed light on the type of space the subway is, its specific social functions, and the nature of embodied social proximity across social differences it affords. On every subway ride, affects arise. To understand these affective transfers and flows, I invoke the concept of contagion as a concern that predates and transformed with the rise of Covid-19. I investigate the various social norms and imaginaries devised to organize the space, considering old and new currents of social exchange, their adaptations and sources, and how they help us manage social proximity in the subway. Finally, I explore methods of surveillance and enforcement and their impact on the MTA workers charged with upholding social norms and enabling solidarity in the subway.