Self found Book I quite a yawn, frankly (aside from the part about how everyone decided to go nekkid during wrestling competitions, a practice begun by the Lacaedemonians, who were enemies of Athens. Why this is even in Book I is a mystery, but let’s not look a gift horse in the mouth)
Anyhoo, Book II begins with the beginning of hostilities between Athens and the Peloponnesians. It’s a very exciting tale. The Thebans decided to take the city of Potidaea, which was an ally of Athens. They were aided in their plot by traitors, who opened the gates to the invaders at night, when most of the citizens were asleep. Anyhoo, the citizens roused soon enough, and realized the enemy was in their midst. They might have said, “All is up with us” and decided to surrender, but (and self finds this believable only because of Ukraine), they decided to fight.
It was still night, though daybreak was at hand: in daylight it was thought that their attack would be met by men full of courage and on equal terms with their assailants, while in darkness it would fall upon troops panic-stricken, who would also be at a disadvantage from their enemy’s knowledge of the locality. So they made their assault at once, and came to close quarters as quickly as they could.
Twice or thrice the Thebans beat back their assailants. But the men shouted and charged them, the women and slaves screamed and yelled from the houses and pelted them with stones and tiles — and besides, it had been raining hard all night — and so at last their courage gave way, and they turned and fled through the town. Most of the fugitives were quite ignorant of the right ways out, and this, together with the mud, and the darkness caused by the moon being in her last quarter, and the fact that their pursuers knew their way about and could easily stop their escape, proved fatal to many. The only gate open was the one by which they had entered, and this was shut by one of the Plataeans driving the spike of a javelin into the bar instead of the bolt; so even here there was no longer any means of exit.— the peloponnesian war, book 11: beginning of the peloponnesian war, first invasion of attica