The battle for Boston is over, but there are still dangers lurking in the city. And as Elizabeth and Thomas arrive, they discover that old enemies are waiting to strike back.

Desperate to find her father, Elizabeth sets out to see if anyone knows whether he survived the battle. She soon learns, however, that the city's new rulers don't take kindly to people digging into the past. Before long, she's thrust into the middle of a deadly power struggle, and she's forced to take a role in a fight she doesn't even understand.

Meanwhile, Thomas and Carter encounter a familiar face. The dead are still walking, and a cure for the sickness is about to fall into dangerous hands. But what is the mysterious Project Atherius, and why are powerful people willing to do whatever it takes to become part of the project's main plan?

Days 109 to 116 is the eighth book in the Mass Extinction Event series. The book ends with a cliffhanger, and readers are advised to start with the first part of the series.