Demeter was the Goddess of Corn. She was the mother of Persephone. Her festival occurred at a temple in Eleusis, and the procession was called the Eleusinian Mysteries. It is generally unknown how the procession is carried out because it was kept a secret.
The god of the Underworld, Hades, had stolen Persephone as his own. Demeter was of course heavily distraught over this. In her grief she left Olympus and traveled down to earth, where she manifested herself as a woman and wandered aimlessly around, lamenting her daughter.
Four maidens sighted her, and they offered to take her in their home. The girls' mother, Metaneira, welcomed her. Demeter nursed Metaneria's son Demophoon to become immortal and honored; however, Metaneira witnessed a part of the procedure where Demophoon was lain in an open fire. Horrified, she screamed in terror and angered Demeter. In response, Demeter revealed herself as a goddess and ordered that a temple be built for her in her honor.
Metaneira's husband, Celeus, built the temple and Demeter resided in there at once. During her depression, crops failed to grow and many civilians feared they would die from famine. Zeus intervened and sent Hermes down into the Underworld to retrieve Persephone. Hades gave her up, but not before making her eat a pomegranate seed, forcing her to come back to him eventually.
Persephone and Demeter finally reunited, and at once Demeter apologized for the period of lifelessness, and she restored the crops to their former glory. However, now Persephone had to return to the underworld every winter, and then reemerge in the spring. Demeter would from then on have to deal with this dilemma, and she would mourn every winter for her daughter.