After centuries of plotting, the Sphinx — leader of the Society of the Evening Star — is after the final artifacts- the Chronometer and the Translocator -needed to open the great demon prison, Zzyzx. If the legendary prison is opened, a tide of evil is certain to usurp control of the world. In an effort to intercept the final artifacts, Kendra, Seth and the Knights of the Dawn race to strange and exotic preserves across the globe. The stakes have never been higher. The risks have never been more deadly. In this explosive series finale, allegiances will be confirmed and secrets revealed as the forces of light and darkness collide in a desperate, climactic battle to control the keys to the demon prison.
Kendra, Seth, and the Knights of the Dawn continue to take the last possible steps to safeguard the keys and locks placed on Zzyzx. Graulas asks Seth to recover the Sands of Sanctity so he can die peacefully. Seth agrees to ease his suffering. They go to Obsidian Waste, the preserve in Australia. They are welcomed by the caretaker Laura and the twins Camira and Berrigan. Laura quickly kills Camira and reveals that many members of the Society are waiting to ambush them. Several members of the Society appear and the group quickly flees to the Obsidian Vault where the Translocator is hidden. After a series of trials they get the artifact, only for the society to capture them. Seth, Mara, and Berrigan are captured.
Trask, Tanu, and Kendra escape with the Translocator. Meanwhile, Seth is summoned to talk with the Sphinx. The Sphinx reveals that they are in Living Mirage the fifth secret preserve, and he is the caretaker. He also tells Seth that he is a shadow charmer and has the Font of Immortality, the last artifact. He takes Seth to Nagi Luna, a demoness who aids the Sphinx (but secretly wishes to betray him and open Zzyzx on her terms) Seth befriends Bracken, a unicorn with no horn. Bracken is stuck in human form due to him giving up his horn to make the Font of Immortality. Meanwhile, in Fablehaven,Vanessa reveals her secret, Grandpa and Grandma Larsen are alive and they are undercover spies for the Knights of Dawn. They plan on a rescue mission, however they are captured by the Sphinx, thus giving the society 4 artifacts.
Kendra goes to commune with the Sphinx. While Kendra is talking with the Sphinx. A mysterious figure gives Seth a sack containing the Translocater and the Sands of Sanctity. Seth escapes to Fablehaven and uses the Sands to heal Graulas. Graulas grows strong and takes the Translocater and the Sands from Seth. He reveals that Nagi Luna was the one who orchestrated Seth's receival of the artifacts. Kendra gains two new allies and finds an old friend during her extremely short visit in the same cell as her brother had been. The three, Kendra, Warren, and Bracken, take the very last, final steps to prevent the demon horde from escaping. Their problem: they would be trapped inside the preserve without outside help. Their troubles include a tempting yet lethal grove of trees, a roc parent, a real sphinx, and some furious harpies. On his journey, Bracken finds an "old friend." After retreating over the preserve's wall, the three race to beat the Society to the final locks that hold Zzyzx shut.
Meanwhile, Seth is coping with a friend's death and a betrayal back at Fablehaven. Patton Burgess, in a gaseous form, suggests some truly desperate ideas to oppose the demon horde. Seth must call upon his loyalty, devotion, and his unique traits to gain a powerful weapon, a remnant from an age of wonders that may save the world. When all of the demon prison's locks were undone, the hour had arrived to unite. They all meet up at the place where the ship Lady Luck will take them to Shoreless Isle. They use the items to summon the Lady Luck. Seth uses force to convince the ghost of the Lady Luck to take them there. They find a Shrine to the Fairy Queen near Zzyzx. When Graulas and Nagi Luna begin to open Zzyzx, the dome of the demon prison cracks, and the Battle of Zzyzx begins. Kendra and Bracken speak once more to the Fairy Queen, who tells them that she has destroyed all of her other shrines, and they have one final secret plan that may just grant success. The astrids' get their original humanlike forms back. Bracken needed the five artifacts, so Seth, some astrids, and the Sphinx transport into the dome and reclaim the artifacts. After evacuating her world, the Fairy Queen traps the demons into her realm, and makes Zzyzx her new home. After a success on the battlefield, Kendra, Seth, and all creatures of Light must wait to see whether Bracken's plan would work and whether the world would live to see a dawning of a new age of security, when Kendra can finally find peace and joy and reclaim a life even better than the one that was stolen from her (or so she hoped). After that, Kendra is relieved in joy because her family is released.
Release date controversy
The release date was planned to be March 23, 2010; however, some major booksellers started selling copies on March 19, 2010. Shadow Mountain, the book's publisher, was alerted of this later that day, but thousands of copies had already been sold. Due to this, after receiving apologies from the booksellers, Shadow Mountain allowed the booksellers to continue selling copies, and changed the official release date to March 19, 2010.