At first glance, The Book of Jeremiah has no real order to it. It jumps back and forth through time, and includes different kinds of material: prophecies attributed to Jeremiah regarding Judah's doom, stories about Jeremiah himself, and poetic passages attributed to Jeremiah about the bloody fate of other nations. There are also passages where, rather than prophesying, Jeremiah laments his sufferings as a persecuted outcast, going so far as accusing God of abandoning him and wishing he'd never been born. It's hard out here for a prophet.
In spite of the lack of chronological order in the actual text, we'll summarize Jeremiah's story in brief. Jeremiah's called to be a prophet by God when he's just a boy. From there, he goes onto a long and illustrious career, prophesying total destruction and angering the kings of Judah, who definitely aren't interested in hearing about their imminent and gruesome demise.
The central message of all Jeremiah's prophesying is Judah's inevitable destruction and exile by the Babylonians at the hands of a very wrathful God. While he's making these terrifying predictions, Jeremiah has to deal with kings who want to imprison him or execute him: King Jehoiakim tosses a copy of Jeremiah's prophecies into the fireplace, and King Zedekiah gives people permission to kill him (though he also helps save him—go figure.)
Eventually, Judah and Jerusalem are ransacked and burned just like Jeremiah had been saying all along, and most of the population gets dragged off to Babylon. Jeremiah stays behind at first, but winds up reluctantly going to Egypt with a bunch of Judeans who—according to God—are also doomed to perish when the Babylonians continue their murderous ways and attack Egypt.
In contrast to the doom-and-gloom narrative of most of the book, chapters 30-33 are known as the "Book of Consolation," These are God's words of hope and comfort, four chapters of mercy surrounded by forty-eight chapters of stomping-around divine wrath. Jeremiah, speaking with God's voice, predicts that the people will be led back to Judah, but this time things will be different. They'll worship God with full devotion, and won't just go through the motions while actually wishing they were home watching "Real Housewives of Jericho." On the inside and the outside, the people of Judah will be in a real relationship with their God.