Hades kidnaps Persephone and takes her to the underworld.
Earth and mankind are dying and Demeter refuses to fix them until she can see her daughter again.
To save the earth Hermes brings Zeus's message to Hades and Persephone is released.
For the rest of eternity four months out of the year, Persephone must spend time with hades. When she goes into the underworld nature dies creating winter and when she returns Nature comes to life again.