As soon as Zuko's leg was healed enough for him to walk around without being in pain anymore, Iroh decided it was time for him to train his son and nephew. Therefor Zuko's and Katara's time together was cut really short, since Iroh would have Lu Ten and Zuko practice their firebending the whole day. In the evening, both of them were too exhausted to do anything else than going to bed. So Katara was preparing the revenge on Lu Ten on her own.
Lu Ten managed to use new learned moves far quicker than Zuko, and he also managed to create lightning, which Zuko simply couldn't. It would blow up in his face, whenever he tried. So Iroh taught him how to redirect lightning by using waterbending-techniques. He had invented the move himself, so no one else knew it, despite Iroh and now Lu Ten and Zuko. Though Iroh wouldn't allow them to test it and said he hoped they would never have to use it, for it could easily kill them, if they would make a wrong move. As he released them that day, both of them were far too interested in testing out their new move that they couldn't go to bed right then. But Iroh caught them in their attempt to test it on each other and got really angry at them. So they were sent to their rooms to meditate about what they have learned.
Of course Zuko's meditating was cut short by Katara's visit. "The plan is ready." She told him. "Tonight then?" Zuko asked back and Katara nodded. "By the way, my brother is still lurking around…" she added. "Yes, I know…" Zuko smiled "He is trying to figure out how he could sneak on me without being burned to a crisp." "Did you attack him?" Katara asked confused. "No, but he tried to sneak in on me last night, and I happened to hear him…" Zuko explained "I think he was kind of spooked by the fireball I had in my hand as soon as I heard him. At least he screamed and smashed the door shut behind him as he left…" "He's such an idiot, sometimes…" Katara sighed.
At midnight the two of them met again right outside of Lu Ten's room. They had both clad in black hoodies, making them hard to spot in the night-dark ship. Each of them carried a bucket with snapper-clams inside. Katara had collected them over the past few days from the ship's belly with waterbending them up on deck. She had kept them in buckets with fresh water, but still they were kind of smelly and slimy and they bit if one dared to put one's finger in there. "Ready?" she whispered. Zuko nodded. Carefully he opened the door to Lu Ten's room and the both of them snuck into it, carefully closing the door again behind them. Lu Ten was fast asleep. As soundlessly as possible, they put down the two buckets with snapper-clams next to his bed and snuck back to the door.
Once out of the room, Katara used her waterbending, to raise the clam-filled water out of the buckets, and hovered it over sleeping Lu Ten, before she released her grip on the clam-filled liquid. As soon as she had done so, she jumped back, Zuko slammed the door shut, and both of them started running towards their rooms. Lu Ten's cries of surprise and rage followed them through the dark hallways. It was not long until the noise had woken every last member of the crew. They had reached Zuko's room just in time and now leaned against the door gasping for air, listening to the tumult that had started outside.
Their plan had one fault though… No one expected Aang to do something like that to anyone, and despite of him there was only one waterbender on the ship left. So Katara was suspected as the culprit right away, and as they went looking for her, they found her with Zuko, so it was kind of obvious they had been in it together. No one was very happy about what they had done. They were dragged apart by Hakoda and Iroh and it was decided that they obviously were bad influence on each other. Therefor they weren't allowed to be in the same room together, with not at least one other person present. Both tried to protest, but were dragged to their rooms and sent to bed by their legal guardians.