Follow a 30-year-old sea turtle as she swims 9,000 miles from the west coast of Mexico to lay eggs on the Japanese beach where she was born. Guided only by instinct, our reptilian hero faces no shortage of obstacles: menacing hammerhead sharks, furious typhoons and human-made booby traps such as fishing hooks and nets. But she will also witness undersea kingdoms of breathtaking beauty in this episode of the acclaimed PBS "Nature" series.