The Lightning Thief
by Rick Riordan
Demeter is Zeus's sister and the Goddess of Agriculture. She makes sure things grow and that crops are bountiful. Her daughter is Persephone, Hades's kidnapped wife. When Persephone was first kidnapped, Demeter was heartbroken and travelled all over the world trying to find her. During that time, farmers everywhere had it rough, because no one was looking out for them and their crops. Persephone and Hades worked out a plan for their marriage: Persephone would spend six months of the year with him in the Underworld, and six months of the year with her mom, above ground.