The heroes are on vacation. Really. The wedding of Dane and Annabeth (Danabeth) is over, the team has caught their villain-of-the-month, and Hope thinks everyone deserves a break from the cycle of training and public-relations appearances. So except for Ozma and Grendel (who've decided to return to adventures in Oz) they're all enjoying the sand and the sun in Littleton, the safest secret community in the world.

But then Shell vanishes—her quantum-neural link with Hope and Shelly severed—and Ozma and Grendel return with ominous warnings that something is happening back in Chicago. As the Young Sentinels race to return home, the city is attacked by old and new foes and the fight does not go well. Heroes fall, and the survivors are faced with threats unlike any they have faced before. The Post-Event World is entering a new period of conflict, and Astra and the Sentinels must answer to their motto, Nos Preaestolor; We Stand Ready.

Fortunately, they don't stand alone.