This is the first history book in Western history.
Book One
Paris is motivated to abduct Helen because of the rapes of Io, Europa, and Medea. This is the start of the Trojan War. He explains who is powerful in Asia Minor, including Candaules, Gyges, Alyattes, and Croesus, among others. Then he details a specific story about Candaules.
Candaules asks Gyges to see his wife naked, but his wife freaks out (appropriately) and demands that one of them die. Gyges seizes the throne and conquers Candaules in combat. Also, there's a story about a person riding a dolphin. Herodotus mentions other minor stories, like who the happiest man is, and some other minor stories about Asia Minor's kings.
He explains the Oracle of Delphi's prophecies about Croesus attacking the Persian army. We meet a bad king who reigns and dies in Athens named Peisistraos. We learn about the rise of Sparta. Other various Persian history is recalled, to explain who the enemies will be when they go to war. Also mentioned is the kingdom of Babylon in Assyria. To end Book One, the story is told of Cyrus's attack against Babylon, which he wins before dying in his next combat.
Book Two
There is an experiment to begin this book to prove the age of Phrygia. In the experiment, children are deprived of language.
This book begins with a brief, basic history of Egypt. The Nile is the main reason the kingdom exists, in Herodotus's opinion. The animals of Egypt are horrifying: cats, crocodiles, hippopotamuses, pythons, and cobras all live in Egypt. Those animals are not native to the Greeks, and they're very scary in any case.
The story returns to Helen and Paris. She stays with him, causing the Trojan War.
After this, we learn some Egyptian history, like Cheops building the Great Pyramid of Giza, using revolutionary machinery. We learn of the line of priests in Egypt, and we learn about how sacred labyrinths are in the Egyptian world, because they believe a labyrinth awaits us in the afterlife.
Book Three
Persia attacks Egypt under Cambyses II, and they overthrow the Egyptian king Psammetichus III. We learn about Cambyses's madness after his attack on Ethiopia. Herodotus tells of the king of Corinth who hates his son. When two Magi rebel against Cambyses, he is killed.
Darius I comes to power in Persia. We learn who the satraps are in Persian government.
Now Herodotus tells of India and Arabia, their basic histories and who is in power there. After some stories about minor characters, we learn that Babylon was defeated by a clever man named Zopyrus.
Book Four
The Scythians are described, and their history. There is the story of Aristeas, the powerful poet. The regions of Scythia are described (the region north of the Black Sea). Africa (called Lybia), Asia, and Indo-Europe are compared and contrasted by Herotodus. The culture of the Scythians is insular, skeptical, and often very strange to Herotodus.
Darius attacks Scythia and declares war. Some nearby religions are described, including some fairly violent forms of sacrifice and worship. When Darius fails to conquer Scythia, Scythia forms alliances with the Amazons.
We learn what became of the descendants of the Argonauts and their founding of Cyrene. The kings of Cyrene are listed in order, and then there is a list of African people groups.
Book Five
The Thracians are attacked by Megabazua, and the Persians respond to violence against Persian merchants by Macedonians. Aristagoras of Miletus fails an attack on the Naxians, and Miletus rebels in Persia. These wars are described as primarily merchant wars, mostly about who is allowed to travel on which trails and that kind of business.
We learn how the Greek learned to form their alphabet by buddying up with the Phoenicians. When Athens is attacked, Sparta saves them, but then because they are weak, Sparta harasses Athens, too. There is a town burning in Sardis, and Darius vows revenge against Athens.
Meanwhile the Persians realize they probably won't be able to hold off the Greek rebellion for much longer.
Book Six
In preparation to fight against the Persians, the Ionian army receives help from Dionysius of Phocaea. They are defeated at sea. When Mardonius attacks Greece, he conquers Macedon and enslaves them. Athens summons help from Sparta again, and some Spartan history is told explaining why they always have two kings, and how they divide up responsibility.
Demaratus of Sparta is impeached for lying about his ancestry. Cleomenes is driven mad by constant assassination attempts and he kills himself.
There is a story about a man named Pheidippides meeting the god Pan on his way to request back up from Sparta. The Athenians win at Marathon, but mostly without Sparta's help. Sparta is late to the battle. They attack Paros and fail, but they do take Lemnos.
Book Seven
Darius learns about the loss at Marathon. He decides not to give the throne to his son when he dies, giving it to Xerxes I. He dies, and while the Persians are weak, the Egyptians attack Xerxes's army. Xerxes uses infrastructure to bolster his forces.
Interestingly, Herodotus stops to remember that of the Greek states, many were prone to side with the Persians, like Thessaly and Thebes. When the nations try to meet for diplomacy, their efforts fail. This precipitates in the Battle of Thermopylae where the Greeks hold a narrow pass for three days with only three hundred men or so. The Greeks are defeated and retreat. Xerxes defeats them again and commands his army to decapitate Leonidas and hang his body from a cross.
Book Eight
Eurybiades replaces Leonidas. A storm destroys a fleet of 200 ships. The gods are given credit for the salvation of Delphi from Xerxes. Eventually, Xerxes's army gets close enough to Athens that they evacuate the city, and do battle at Salamis, and since they can swim, they survive when their ships go down, but the Persians often sink because they don't know how. In Persia, we learn of Artemisia, a priestess who serves the military as counsel.
Themistocles leads the attack on Andros, and Xerxes barely escapes, and in the process, he loses access to an entire army that he had hired. Alexander I of Macedon takes center stage, and we learn his ancestry, and we learn of his decision to stay at war with Persia instead of seeking peace.
Book Nine
The Persians ransack the city of Athens again, but again, the Athenians were clever enough to evacuate to the wilderness. Thebes is also evacuated. During a skirmish, the Greeks kill an important Persian calvary leader named Masistius, and they meet up with Alexander I who tells them they know of an impending Persian attack. They do battle against the Persians at Plataea and win, splitting the spoils. Artabazus of the Persian army escapes into Turkey in the chaos of battle.
Finally the Greeks push the Persians out of Ionia in the Battle of Mycale. We learn an unpleasant tale about Xerxes's wife torturing and mutilating the wife of Masistes. When Masistes responds to this heinous betrayal, he is murdered.
The Athenians win two small skirmishes, and it becomes clear that the war is over.
