Captain Justo, Valley of Bones, continues the adventures of Captain Justo and the Sterling family. After being swallowed by a black hole into a parallel dimension, Captain Justo meets the High King of Atlantis and is charged with rescuing the Sterling family. After doing so the High King reveals that he was known on Earth as Merlin the Magician and chooses Captain Justo as his successor. Uncle Cenric reveals that he has sworn loyalty to King Alhred, usurper of the Seratian throne and will kill them if they return to Seratia. The arrival of Captain Justo and the Sterling family in Seratian territory awakens Incatez, the Destroyer of Worlds, and his immortal army. How will they save all of humanity from an invincible foe?