As the first year of the crisis comes to an end, dark forces battle for the future of humanity. War is coming, and Thomas soon finds himself drawn into the battle that's raging outside Project Atherius. As he and his sister try desperately to survive, they discover that the secret to the entire project might be hiding in an unusual place.

Meanwhile, Elizabeth discovers the awful truth about someone she loves. Project Atherius is about to be unleashed, no matter how many lives have to be lost in the process. Separated from her father, Elizabeth soon receives help from an unexpected source, but how much of her own mind will she have to sacrifice in the process?

Days 357 to 364 is the twelfth 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.