Book #19, The Quest of the Missing Map , where Nancy searches for a treasure hidden by a seafaring grandfather.
The plot centers on , the "Fifth Turtle," and his older brother Walt . [S3E40] The Missing Map
If you were thinking of a different series, "The Missing Map" is also: Book #19, The Quest of the Missing Map
Fans often point out the plot hole of why the Turtles would even keep a physical map to their own home if they wanted to keep it secret. Walt's plan backfires when he attempts to sell
Walt's plan backfires when he attempts to sell the map to Shredder and Krang. Shredder doesn't just want the lair—he also uses the opportunity to steal a document that reveals the truth about Oroku Saki's past with Hamato Yoshi.
The episode features a rare sequence where Michelangelo walks the boys through a convoluted path to ensure they can't easily find the lair again—showing the Turtles actually do care about security.