The Quest For Pan was a quest led by satyrs to find the god Pan when he disappeared over two thousand years ago. He disappeared due to nearly all of his wild kingdoms on Earth being destroyed and violated by mortals.
Two thousand years ago, Pan knew that his realm was being destroyed. He told a satyr named Lysas to spread the word that the great god Pan was dead. Mankind and other species believed this and began further destroying the places of the wild. Satyrs, however, never believed that their god was dead and began searching the world for the god of the wild. Because of their faith, Pan was unable to fade, but would sleep for long periods of time waiting for a satyr to once again take his message out into the world.
Grover Underwood explained to Percy that he wants to be a searcher so he can go and find the god Pan, just like his father and his father before him. However, no one has ever come back from this quest, but Percy believed that if anyone could find Pan, it would be him. On their quest to find Zeus' Master Bolt, they ran into Medusa's lair, where Grover finds a statue of his Uncle Ferdinand, a searcher who was also looking for Pan, but was turned to stone.
After returning from the quest, Grover is awarded a searcher's license and he goes out into the world to look for Pan.
Grover's search for Pan eventually lead him down to the Sea of Monsters off the coast of Florida in the Bermuda Triangle. He was lured there by the Golden Fleece, a magical item with the strong smell of nature magic. There he met Polyphemus, a cyclops that had used the fleece's magic to enrich his island, but also to lure satyrs there so he could eat them. Grover managed to escape and send a distress call to Percy using an Empathy Link, but was recaptured by Polyphemus.
Back at Camp Half-Blood, Clarisse La Rue was given a quest to find the Golden Fleece to save Thalia's Tree, while Percy, Annabeth, and Tyson followed behind to find Grover. They eventually defeat Polyphemus, and retrieve the Golden Fleece. While not finding Pan, Grover was rewarded for clearing the way for other satyrs in the future who would go and look for Pan.
While not currently searching for Pan, the god of the wild sent a Erymanthian Boar as a wild blessing near Cloudcroft, New Mexico. After finishing their current quest to free the god Artemis, Grover sent out satyrs near the town to see if they could find any trace of Pan, which they didn't. Grover, however, did receive a message from the god, saying, "I await you."
Because Grover was still unable to find Pan, the Council of Cloven Elders gave Grover a deadline to find Pan, or his searcher's license would be revoked. To try and prevent this, Grover agreed to go on a quest into the Labyrinth, as the prophecy talked about finding the "lost one."
While in the Labyrinth, the group agreed to run an errand for Hephaestus by figuring out who was using his forge, in exchange for information. On the way to the forge, Grover found a tunnel that he believed to be the way to Pan. While Percy said they would come back later, Grover argued that the passage wouldn't stay open forever. Tyson agreed to go with him to help and the group split up.
Later, when Percy returned to Camp Half-Blood after spending some time on Ogygia with Calypso, he found out that the council had revoked Grover's license and he would be shamed once he returned. Percy and Annabeth return to the Labyrinth with the help of Rachel Elizabeth Dare as their guide. Percy had a dream that Tyson and Grover where still looking for Pan, but were attacked by a Giant Snake. The group eventually meet up in Carlsbad Caverns, a cave system in New Mexico, close to where Grover felt his presence when the Erymanthian Boar appeared.
The group approached Pan, who was surrounded by animals and plants of the wild that had been extinct for many centuries. Grover, overjoyed, said that Pan could save the wild, but the god explained that his realm was beyond saving and he was only kept alive by the belief of the satyrs. Instead, he told Grover that he should go and protect the remaining wild places and that he could no longer wait for a god to do it for him. He had chosen Grover as he believed in Pan more than anyone else, so Pan told him to spread the word once again that the great god Pan is dead.
Grover accepted this role and when Pan died, he gave a little of his spirit to Grover, Tyson, Percy, and Annabeth. When Grover told the Council of Elders that Pan had died, they denied the fact and claimed Grover was speaking blasphemy. When the Titan army attacked Camp Half-Blood, Grover used Pan's Panic shout that scared off the rest of the army concluding that he had received more of the spirit of Pan than the others.
After the battle, the Council of Cloven Elders voted on Grover's fate, as they wanted to put him into exile for his claims. The vote however ended in a tie (as Mr. D claimed that as a god, his vote counted twice) and no decision was issued. However, Grover still left and went to spread the word that the wild places of the world need to be protected and eventually rebuilt.