2 Kings begins just where 1 Kings left off: Ahab is dead, and his house and his queen, Jezebel, are awaiting their destruction—which has been delayed for the present (although Ahab's son Ahaziah dies after falling through a lattice). Meanwhile, Elijah hands off the mantle of his prophetic role to Elisha, before departing for heaven in a whirlwind and a chariot made of fire.
Elisha launches a successful prophetic career, similar to that of his master. He brings a child back to life, makes iron float, magically purifies poisonous food, kills a pack of irritating children by sending bears after them—you know, normal prophet stuff. He also helps save Israel from the Aramean army, temporarily blinding them and then treating them to a feast before releasing them (aw—sweet, right?). He also helps end a famine that has been inflicting Samaria.
However, cool as the prophets are at this time, Israel and Judah both need to deal with a number of horrible kings—Jehoram and Ahaziah being but a couple of the culprits. Jehu, a soldier ordered to rebel by God, ends up dispatching both those guys. He also finishes Jezebel off: her eunuchs chuck her out a window, and then dogs eat her corpse (ew). But Jehu himself is an imperfect king of Israel, continuing to follow the "sins of Jeroboam" from 1 Kings. Judah gets a rather better king, Joash, to whom Elisha gives sage advice, and who helps vanquish some more of Judah's enemies.
Eventually, Assyria destroys the northern kingdom of Israel. Thanks to the persistence of Jeroboam's sins and other idolatries, the ten tribes are being scattered and moved to other places. Assyria attempts to destroy Judah as well, but thanks to God's intervention, the Assyrian army is slaughtered by an angel before they can enter Jerusalem. The righteous king, Hezekiah—who is supposed to be one of Judah's very best rulers—survives. Thanks again to God's help, he manages to tack another fifteen years onto his life and reign on after nearly dying.
Yet, again, bad follows good, and the wicked king Manasseh starts doing all sorts of idolatrous things again like sacrificing some of his own children in fire (presumably to Moloch). Despite the best efforts of the super-good teen king, Josiah, God's wrath is kindled against Judah. Whereas the Assyrians had crushed Israel, King Nebuchadnezzar of Babylon invades Judah as the story ends, destroying the country and sending the majority of people into exile in Babylon. Bad times.