Cigarettes and Late Night Train Rides

In the distant future sea levels have risen, swallowing up all of the continents. The remainder of the population now lives together in a 100 story mega building, each floor housing its own city with its own population and economy; the higher the floor, the wealthier the city. A group of friends from the city on Floor 19 lose one of their own to suicide. Or is it something more sinister? A fast-paced journey from bottom to the top of the structure will provide answers to their burning suspicions.