What is the title of the two-part episode that ends Book One?

The two-part episode that ends Book One is titled “The Siege of the North.”

This season finale follows Aang, Katara, and Sokka as they defend the Northern Water Tribe against a major Fire Nation assault. Admiral Zhao commands the invasion, while Prince Zuko secretly enters the city in an attempt to capture Aang. The story brings several season-long conflicts together in one large-scale battle.

The finale is split into Part 1 and Part 2 and is listed as episodes 19 and 20 of the first season. Its central supernatural conflict involves Zhao’s attempt to destroy the Moon Spirit, which threatens the balance that supports waterbending. Aang ultimately enters the Avatar State and joins with the Ocean Spirit to repel the attack.

Viewers sometimes confuse the title with “The Waterbending Master,” the preceding episode, or “The Blue Spirit,” an earlier Zuko-focused episode. “The Siege of the North” is the finale’s complete title, and the story takes place at the Northern Water Tribe.