Readers immersed in Morgan's dystopian series will find Day 21 ferring to the time it takes for radiation sickness to appear after exposure welcome sequel to the series opener. Kass follows the stories of the half dozen major characters who have landed on earth after living aboard ship-bound space colonies, as they make their first face-to-face contact with the descendants of humans who never made it to the space colonies. Backstories, in addition, fill in details of how the characters ended up on the drop-ship in the first place. A new character, earthborn Sasha, brings a new and compelling strand into the spiraling plot of sons and daughters whose parents' politics have condemned them to beginning civilization anew.

In the sequel to The 100, the hundred are reeling from the surprise that they aren't alone on Earth. While in space, serious problems with the ship cause the colonists to contemplate abandoning it. In chapters alternating between characters' perspectives, inconsistent plotting and emotional development strain credibility, but readers who enjoy their sci-fi with romance and drama will still be plenty entertained.