This essay offers an archipelagic reading of Walter Mosley’s detective novel Down the River Unto the Sea (2018). I argue that the spatial imaginary of the novel constitutes a layered map of the Americas that registers continental visions of the US nation-state but cognitively remaps and breaks up this space into various archipelagic constellations. I read the novel as contributing to a specifically African American mode of the archipelagic, which I trace along two trajectories: a focus on carceral archipelagos and im/mobilities, and a negotiation between what David Chandler and Jonathan Pugh have called “interstitial” geographies, which focus on relationality, and “abyssal” geographies, which posit and critique antiblackness as the world’s foundational violence. In my reading, both trajectories sit firmly within the concerns of archipelagic studies but significantly extend the paradigm’s scope. The first trajectory depicts the US nation-state both as imperial continent and as racialized carceral archipelago and sets these layers off against visions of fugitive archipelagos that afford Mosley’s characters temporary islands of safety or respite, but never grant them the contiguity that undergirds Western fantasies of nation-state sovereignty. The second trajectory employs both interstitial and abyssal analytics to address the question what an "imagined community" can mean in a starkly antiblack world. Via the intertwined stories of two protagonists, the detective Joe King Oliver and the prisoner A Free Man, Mosley’s novel envisions African American responses to systemic betrayal within the US—being sold Down the River—and pushes, geographically and ideologically, beyond constellations of the nation-state and citizenship—Unto the Sea.