If you were thinking of a different series, "The Missing Map" is also:
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. [S3E40] The Missing Map
Walt, envious of the attention his brother gets from the Turtles, steals a rare pouch containing the only physical map to the Turtles' secret lair. If you were thinking of a different series,
The plot centers on , the "Fifth Turtle," and his older brother Walt . the "Fifth Turtle