Zephaniah

The prophet Zephaniah was active during the reign of the good, reforming King Josiah (640-609 B.C.). He spoke the word of the Lord to the Southern Kingdom of Judah, since the Northern Kingdom of Israel had already fallen to the Assyrians in 722 B.C. He was a contemporary of the prophets Nahum, Habakkuk, and Jeremiah.

Here is the outline of the book from the ESV Study Bible:

I. Heading (1:1)

II. Judgment Coming Against Judah (1:2-6)

III. The Day of the Lord (1:7-3:20)
     A. Day of sacrifice and punishment (1:7-9)
     B. The coming wrath (1:10-18)
          1. Against God's people (1:10-16)
          2. Against all humanity (1:17-18)
     C. Repentance is still possible (2:1-3)
     D. Nations warned (2:4-3:8)
          1. Philistines (2:4-7)
          2. Moab and Ammon (2:8-11)
          3. Cush (2:12)
          4. Assyria (2:13-15)
          5. Jerusalem (3:1-7)
          6. Summary (3:8)
     E. Anticipation of hope (3:9-20)
          1. Conversion of the nations (3:9-10)
          2. Judah's return (3:11-13)
          3. Joyful song (3:14-17)
          4. God's promised restoration (3:18-20)