As New York is destroyed, Elizabeth desperately tries to find a way out. She eventually heads down into the subway system, hoping to at least escape from Manhattan, but she soon finds that she's not alone. Deadly creatures lurk in the dark tunnels, and Elizabeth is quickly plunged into a fight for survival. Zombies aren't the only danger, either, as swarms of rats hunt for their next meal.

Meanwhile, hundreds of miles away, Thomas starts to learn the truth about his sister. Martha might have survived, but she's acting strangely and it soon becomes apparent that she's hiding something. How will Thomas react if he's forced to choose between his sister and his friends?

Days 203 to 210 is the tenth 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.