When last we left Doctor Hanover at the fort of Turtle Island, she and Master Rogers had survived the night protecting the fort from the marauding Hot Animal Machines, becoming comrades in the process. Their numbers decimated, the invaders chose not to flee, but to make camp outside of rifle range and harass the fort, making it impossible to graze their livestock and impossible to leave.
Eager to leave above any other motivation, Doctor Hanover reluctantly agreed to deliver poisoned opium to the Hot Animals as a decoy, a deadly "tribute."
Unbeknownst to anyone, Master Rogers had begun to rely increasingly on medicinal opium for the pain of a wound he received in Chapter 1. In his shame, he secretly stole some of the poisoned opium and only came to understand his potentially fatal error as he is asked to protect Hanover on her delivery run.
Now, we find ourselves staring down the barrel of Chapter 4: Heroic.
The physician remains the killer.
The warrior becomes her patient.
And a new threat is found among the bones of the old.