The "Heart Attack Letter" in Mayor of Kingstown is a small but important document that spells trouble for anyone who receives it. Mayor of Kingstown season 1 ended with a massive prison riot that had been long boiling. While officers Kyle McLusky (Taylor Handley) and Ian Ferguson (Hugh Dillon) are at the Kingstown prison to transfer Milo (Aidan Gillen) to the DAs office, a riot breaks out, and the two have to crawl into an air vent to wait for rescue.

Kyle manages to get a message off to Mike McLuskey (Jeremy Renner), who sends in Robert Sawyer (Hamish Allan-Headley), and his extrajudicial Swat team. To rescue Kyle and Ian, Robert and his team are forced to kill some of the prisoners, though they take no pleasure in doing so. These events occur in the season 1 finale, "This Piece of My Soul", but it isn't until a few episodes into season...