Jonah was called by God to prophesy against Nineveh but disobeyed and boarded a ship to Tarshish. A storm arose and Jonah was thrown into the sea, being swallowed by a large fish. After repenting inside the fish, Jonah was vomited onto dry land and went to Nineveh, prophesying its destruction. The Ninevites repented, sparing the city. Later, Jonah grew angry that Nineveh was spared and God sought to teach him about divine mercy through a plant and worm. The book highlights God's forgiveness and compassion.