Islands in the Sea: City on a Hill!

Dan, Susan, John, and Nikki answered the call in Islands In The Sea: The King Walks In! Book 1, in the The Lion Roars! Book 2, and then again in Illegitimate? Book 3, but now that one-third of the city is destroyed and under water, can they save the rest of the it. The cult is seeking revenge and the dark sentinels have moved to a better vantage point, but something even bigger and more sinister is approaching quickly in the distance. Can they decipher the coded cave system before it's too ...