Zuko was raised in a nation of secrets. The Fire Sages told elaborate, stylized stories filled with disguises, hidden passages, and a secret river to the palace. Most of this was symbolic, but a fascination with hidden truth permeated the culture. Every character of their mythology wore a mask or veil.
In the palace, Zuko learned that openness was perceived as weakness. He couldn't lie as well as Azula, (he never learned to do anything as well as Azula) so he learned to lie by omission.
Katara fascinated him. How could anyone expose so much emotion and still remain strong? Her sentimental nature could get her killed someday. The necklace she always wore was so obviously treasured that he had once thought she would trade it for the Avatar. He smiled when he thought about that necklace. He had held it so often he could still feel the shape of the pendant in his hand.
He saw Sokka sitting in front of the fire with something delicate-looking in his hand. The water tribe warrior had his tongue sticking out of a corner of his mouth, and a small dagger that he used to scrape away at whatever he was holding. When Zuko asked what he was doing, Sokka replied that he was, "Practicing the manly art of carving." Sokka explained the importance of carving a pendant for an engagement necklace.
When Zuko asked if Katara wore her mother's necklace to show that she was promised to someone in marriage, Sokka laughed. He explained that the tradition had been lost in the southern water tribe. "Besides," Sokka explained, "It's really important for the man to carve the necklace himself."
Sokka explained as he carved. "The men in the northern tribe tell a story of a beautiful woman who had many offers of marriage. The best hunters brought her valuable pelts. Warriors gave her gems taken from the enemy, and gatherers brought her rare, blooming plants. She refused them all. One day, a knife-maker left her a gift. Everyone laughed, because…" Here Sokka paused. He couldn't say that the lame artist was ugly from scars. "because he didn't do any brave deeds to find the gift." Sokka congratulated himself for the save, and continued. "The knife maker had carved a pendant from whale-lizard bone. It was a picture of the woman, dancing. They say that the detail was so good, she seemed to move. He won her, and we've been carving ever since."
"Katara never takes that necklace off," Sokka continued. "Well, actually, she had to take it off so we could disguise ourselves to blend in when we were in the fire nation. Her hand kept going to her neck, and she frowned whenever she felt the fire nation necklace she bought." Then he laughed, "I pity the tribesman who offers her a new necklace. Not that anyone would be foolish enough to marry my sister. He'd have to be a powerful bender, or he'd always be digging himself out of ice," Sokka paused and looked intently at his carving, "a powerful water bender."
Zuko lay awake all night, feeling guilty about having taken her necklace. He was determined to make it up to her somehow. Then he remembered a fire nation legend, about a weapon hidden in a locket.
The next day, he looked for the mechanist's son. Teo agreed to help him. The hinge would be tricky, but Teo was skilled and knowledgeable.
It was almost a week before Teo gave Zuko a functioning locket, made from one of Zuko's gold arm bands. The metal was rough and dull. Zuko polished it with the heat of his hands. It was pretty, but missing something. Zuko smiled while he used a steel needle to scratch a design on the gold. He remembered exactly what the pattern on her necklace looked like, but he couldn't get it right. He kept wiping the metal clean with a hot thumb, and starting over. Then he decided that a water pattern was a bad idea, anyway, and tried to think of something else. He smiled and got to work.
He approached her after dinner. "Katara, Sokka explained about your necklace and – I'm sorry I kept it from you." She didn't even look at him, but she was scowling. Then she saw something shiny in his extended hand. "If you put this over it, you can still wear it when you're disguised as a fire nation colonial." He moved closer. "Please take it, Katara."
Her curiosity overcame her suspicion, and she took the locket from his hand. "How is this supposed to work?" she asked. "Here, I'll show you. Let me have your necklace," he replied. Katara looked uncertain, but she took it off and handed it to him. Zuko opened the locket, and slid it over the pendant of her necklace. It was a perfect fit. He locked it with a small latch, and handed it back to her. "Oh," Katara sounded both pleased and puzzled, "Thank you, it's…it's a really good idea." She looked at him with one eyebrow raised, "What kind of animal is that?" He blushed. "It's supposed to be a turtle-duck in a pond. They're the only thing I know how to draw. You can turn the locket around, if you want. A lot of fire nation women wear plain gold lockets. I just thought, since you are used to a pattern, well, I'll just turn it around for you," Zuko stammered as he tried to take the necklace from her hand.
Katara closed a fist over the locket, "No, I like it. It's just that I've never seen a turtle-duck." She hesitated for a second. It wasn't like he was giving her an engagement necklace. It was an apology, and a useful disguise. It was carved, but...he didn't know anything about that tradition. She put the necklace on. "How do I look?" she asked.
Zuko smiled and answered, "Very fire nation."