The Peloponnesians conduct their annual invasion of Attica while the Athenians, on their way to Sicily, occupy the Peloponnesian territory of Pylos. Sparta’s King Agis attacks Athens’ fortifications there. Spartan general Brasidas demonstrates courage and daring, but the Athenians repel the Peloponnesians’ assault, trapping a garrison of Spartans on Sphacteria, a nearby island. Anxious to ensure the release of their men, Sparta sends envoys to Athens to negotiate for peace. However, in a speech to the Athenian assembly, Cleon urges the city to demand Sparta return territories captured in the previous war in exchange for their men.

In Sicily, the Syracusans prepare to attack the Athenians at Rhegium, while in Sphacteria, Athens’ siege continues without a conclusive result. The Athenians become angry that Cleon encouraged them to reject the Spartans’ peace offer. Cleon blames the failure on Nicias, leading him to cede command to Cleon, who then leads the Athenian allies to victory in the Battle of Sphacteria. The Spartans surrender, shocking the Hellenic world, which had expected the Spartans to fight to the last.