Every few days in New York City, a subway operator stops a train, speaks the phrase "12-9" into a radio, and waits what may feel like an eternity for a police officer to arrive and inspect the train and tracks. In the parlance of the Metropolitan Transportation Authority, 12-9s describe collisions between trains and people. In 2019, the M.T.A. recorded a hundred and ninety-five 12-9s, the highest number in at least a decade. About a third are fatal. "After the 12-9" follows three subway operators through their recovery process after their involvement in deadly collisions, as they battle PTSD, nightmares, and guilt. Although all three of them are left with different feelings towards their jobs, they are united by their collective experience of a very specific type of grief: the emotional weight of a death that one had no power to stop.