Chicago didn't die the way cities usually die — not by fire, not by war, not by the slow hemorrhage of population that empties a place over generations. Chicago sank. The process began in the early 2100s, when Lake Michigan's water table began rising in ways that hydrological models could not predict or explain. The lower levels of the city flooded first — basements, sub-basements, the underground passages and service tunnels that formed the city's hidden circulatory system. Then the ground floors. Then the second floors. The flooding proceeded in stages over decades, each stage prompting a retreat upward. By 2180, everything below the fourth floor in the central districts was submerged. The water was not clean and it was not still. It moved with purpose, finding every gap, filling every void, rising with a patience that made engineering countermeasures feel like gestures.

The people who remained — and people did remain, because people always remain — divided along the waterline. Those who retreated upward call their territory the Stacks. Life in the Stacks is vertical. Buildings are connected by bridges, catwalks, and zip lines strung between upper floors. The streets below are canals now, navigable by small boats but useless for ground transport. The Stacks have a government of sorts, a economy of sorts, a culture that is recognizably urban but compressed into the upper registers of a city designed for horizontal living forced into vertical survival. The Stacks are hard but comprehensible. They are what you'd expect from human adaptation to a bad situation.

The Deep is not what you'd expect. Below the waterline, in the flooded lower floors and submerged streets, there are people. This is not disputed — sonar mapping confirms human-scale thermal signatures in submerged structures throughout the central district. How they survive is disputed. The water in Chicago's lower levels is murky, cold, and contaminated with a century of urban runoff. It is not water that supports human life. Diving teams sent to investigate the Deep have returned with footage of illuminated interiors — rooms that are fully submerged but furnished, lit by sources that the divers could not identify, and in some cases occupied by figures who moved through the water without visible breathing apparatus. The figures did not approach the divers. The divers did not approach the figures. Both parties observed each other through the murk with what one diver described as "mutual recognition and mutual disinterest."

I spent a month in the Deep. I will state this plainly because I have stated it under oath, under medical examination, and under BCI scan, and the results in all three cases were consistent with truthful testimony. I entered the water in the former Loop district using a standard diving rig. I was met by a woman who gestured for me to follow her. She was not wearing a diving rig. She was breathing water. I followed her into a building — the former Inland Steel Building, based on the architectural details — where I found a community of approximately forty people living in fully submerged conditions. They ate. They spoke — sound travels in water, and they had adapted their speech to work with it. They had furniture, tools, social structures. They had been there, by their account, for three generations.

I am not considered a reliable witness. My background includes two episodes of stress-related perceptual disturbance, both documented and both treated. The GLMZ Bureau of External Assessment has classified my testimony as "unverified personal account, credibility compromised by medical history." I accept this classification. I note, however, that my BCI recorded continuously during my month in the Deep. The recordings are intact. They show everything I have described. The Bureau has not classified the BCI data. They have not commented on the BCI data. They have filed it and moved on.