As explained by Apollo in The Hidden Oracle, the Grove of Dodona had been planted by Rhea in the first days of the world and were ancient even when the first generation of Olympians were born. These sacred trees could actually speak and sometimes even issued prophecies.
Hence, in ancient times, the priests of Dodona would take every imaginable care of the trees and channeled the trees' voices by hanging wind chimes in their branches. Given proper care, the trees could divine the future, and therefore served as an Oracle of sorts. (Interestingly, the Grove of Dodona was unique in that it had no connection with Apollo, the god of prophecy, since the trees' powers emanated from Rhea instead.)
Without proper care, though, the voices of the trees would become unfocused and disharmonious, and the grove itself would eventually drive mortals to madness. It must still be noted, though, that Rhea had planted Dodona to serve as a benevolent force, and Apollo confirmed that it had indeed helped heroes in the past: for example, the masthead of the original Argo, which could speak to the Argonauts and give them guidance, was carved from a branch cultivated from one of the sacred trees in the grove by the priests of Dodona.
The original Grove of Dodona was eventually burned by Emperor Theodosius, who ordered the last oak cut down. At some point after the 1860s, once the Olympians had moved to America and Camp Half-Blood had been established, the Grove re-grew mysteriously in the forest around Camp Half-Blood.
On the way to Camp Half-Blood, Apollo (in the form of Lester Papadopolous) passes out after the encounter with the nosoi that attempted to destroy him, Meg, and Percy. While unconscious, Apollo/Lester dreams that he is riding the sun chariot with a woman whom he recognizes, but cannot remember the name of, at his side telling him, "Follow the voices and find the gates." Later in the dream, the sun chariot transforms into a bus, and Apollo (still driving) sees through the rearview mirror a man sitting in the back seat telling Apollo to lead him to the Oracle so that it may be burnt.
After recovering from the blight the nosoi attempted to place on him, Apollo consults with Chiron to discover that three students have disappeared: Ares' son Ellis Wakefield, Hermes' son Cecil Markowitz, and Demeter's daughter Miranda Gardiner. At the time, no one knows where they have gone, but later that day Apollo and his son Will Solace just barely prevent Ares' son Sherman Yang from wandering off into the forest. His behavior clues Apollo in to the fact that the woods may not be all that they seem.
During the three-legged death race in the Labyrinth, Apollo and Meg find themselves at Delphi as they attempt to retrieve the first golden apple. While hiding from the monster Python, they overhear Python and a mysterious man who calls himself the Beast in conversation about controlling all Oracles (but burning the fifth Oracle, the one they cannot control). When Apollo and Meg eventually return to Camp Half-Blood after retrieving their other two apples, they find that the woods have claimed two more campers: Apollo's children Austin Lake and Kayla Knowles. At this point, Apollo has recovered enough memories to inform Chiron that the woods appear to be home to the rogue Grove of Dodona, which everyone (except Rhea, apparently) had previously believed to have permanently been destroyed by Emperor Theodosius.
While attempting to find the Grove of Dodona in the Camp Half-Blood woods, Apollo and Meg stumble across the twin-geyser home of the Camp Half-Blood palikoi, one of whom also had previously vanished into the woods, leaving the other palikos distraught and worried. During the conversation, the palikos unintentionally sends out a signal that attracts several hostile myrmekes to the clearing. During the ensuing battle, Meg gets kidnapped by the gigantic ants that also manage to wound Apollo. After swearing an oath to save Meg from the myrmekes before the day's end, Apollo attempts to return back to Cabin 7 for healing, though on the way he collapses and meets Rhea again in a vision. Once again, the Titan queen tells him to find and protect the Grove and this time hands him wind chimes to be tied at the largest oak to get a prophecy.
Once Apollo has recovered enough to venture back into the woods, he sets out to fulfill his oath to rescue Meg. True to his word, he finds her and frees her from the myrmekes' prison. Gaining the favor of the myrmeke queen, the pair exit the myrmeke hive to find themselves at the gates of the Grove, where they discover the six missing people (the five campers and one of the palikoi) tied up to be used as human torches. As they take in this fact, they are ambushed by the mysterious Beast, who reveals himself to be the Emperor Nero, leader of the shadowy new triumvirate of god-emperors who intend to take over the world, starting with New York as the new Rome. Nero also to Apollo that Meg has been playing a duplicitous part: Nero is Meg's stepfather, though due to his abusive nature he has decieved her into thinking that he is fundamentally a nice person with the Beast as a punitive "dark" side.
Enforcing his commands with the threatening presence of his Germani bodyguards, Nero forces Apollo and Meg to open the gates of the Grove in exchange (so he claims) for the lives of the six people tied up as human torches. However, as soon as the gates are open, the Grove urgently tells Meg that Nero intends to raze the Grove, using the six people as tinder to help spread the fire. Stunned by Nero's double-cross, Meg commands her summoned karpos Peaches to prevent Nero from carrying out his intentions, which the karpos does by snatching Nero's box of matches. Ever resourceful, though, Nero breaks a vial of Greek fire on the ground, pulling out a cigarette lighter. Apollo tells Meg to take the wind chimes into the grove and place them on the central oak, and Meg disappears into the grove. After Apollo summons enough divine strength to clear out the two Germani, Nero lights the vial of Greek fire before fleeing, in a final attempt to burn the Grove.
In a burst of panic, Apollo manages to save the six human torches, but is helpless to do anything as the Greek fire begins to threaten to burn its way into the Grove. Desperate for help, Apollo calls on the woods, and several dryads answer his call, sacrificing themselves to save the Grove, a sacrifice for which Apollo feels deep guilt. Once the fire is out, Apollo enters the Grove to seek out why Meg has not placed the chimes yet. As he walks through, the trees whisper to him discordantly, though some seem to follow a theme. Finding Meg, Apollo distracts her from the overwhelming tree chatter, and she is finally able to place the chimes. Upon accomplishing this, they are given a prophecy by the Grove, one which Apollo is not very pleased to hear.
Once the oak finishes the prophecy, Meg runs away, stating that she is releasing Apollo from his servitude to her (though Apollo refuses to accept this), and fleeing due to her sense of shame and guilt in being manipulated by Nero into working against and endangering Apollo. After Apollo calls the myrmeke queen for transportation back to Camp Half-Blood and the Colossus of Nero is subdued, Chiron asks Rachel Dare and Miranda Gardiner to begin studying the Grove so they can learn how to use its power, especially while the four Apollonian Oracles are still under the control of Python and the triumvirate.
The Grove gave two prophecies to Apollo. One of them is little more than a series of phrases and rhymes that Apollo hears among the chatter in the trees as he enters the Grove. The other is a limerick, given in a form that makes it a true quest-launching prophecy. Apollo and Chiron believe that both prophecies refer to the Oracle of Trophonius.
The First Prophecy
Caves of blue.
Strike the hue.
Serpents and roaches.
Unraveling the Prophecy
At the end of The Hidden Oracle, little is known for sure about the meaning of the prophecy. Apollo and Chiron are of the opinion that the Grove is referring to the but Apollo, Rachel, and Chiron are able to glean the following clues:
- "Caves of blue" is repeated in the limerick prophecy, which implies that the Oracle of Trophonius is located in a cave with a lot of blue in it. Along with the clue in the fifth line of "Indiana," this places the Dark Oracle in the Bluespring Caverns.
- "Westward, burning" fits with Apollo and Chiron's theory that the next member of the triumvirate has control of the mid-western section of the U.S. (which of course lies westward from Camp Half-Blood).
- "Pages turning" is rather unclear, though given that mention is made in The Hidden Oracle of Ella and others at Camp Jupiter making efforts to reconstruct the Sibylline Books, it is quite possible that the trees were referring to the reconstructed texts (which in themselves might re-establish the Sibylline Oracle).
- "Serpents and roaches" fits with the fact that Python and the triumvirate appear to have taken control of the four Apollonian Oracles. Whether the animal names refer to the monster and gods or to literal snakes and cockroaches is unknown.
The Second Prophecy
There once was a god named Apollo
Who plunged in a cave, blue and hollow
Upon a three seater
The bronze fire eater
Was forced death and madness to swallow
Unraveling the Prophecy
- "There once was a god named Apollo" is fairly obvious, as the entire Trials of Apollo series is centered around Apollo's quests to reclaim his godhood.
- "Who plunged in a cave, blue and hollow" fits with the previous prophecy, implying that the Oracle of Trophonius is located in the Bluespring Caverns.
- "Upon a three seater" appears to be a reference to Festus carrying Apollo, Leo, and Calypso in their quest.
- "The bronze fire eater" again appears to be a reference to Festus.
- "Was forced death and madness to swallow" is a reference to when Meg (whose body had not been prepared for the Oracle of Trophonius) begins to go insane and starts foaming at the mouth (an implication that she is going to die). Apollo sucks bee venom which is making Meg insane out of her mouth.