Having finally met for the first time, Elizabeth and Thomas soon find themselves in mortal danger as the Mass Extinction series continues.

Having encountered a strange little girl they found at the side of the road, Elizabeth and Thomas follow her to a seemingly abandoned old hospital. They soon discover, however, that something deadly lurks in the shadows, and that the little girl is hiding a terrible secret.

Beneath the hospital, a horrific experiment is being carried out, and a familiar face is involved. While Thomas tries to understand Sarah Carter's aims, Elizabeth finds herself being drawn into the experiment and soon faces a fight for her life. A cure for the zombie outbreak is tantalizingly close, but sacrifices will have to be made if humanity is to have any chance of survival.

Days 101 to 108 is the seventh 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.