As soon as everyone was aboard the ship, Zuko set sail for Crescent Island, the location of the Fire Sages Temple, where Avatar Roku was enshrined. According to Iroh, if Aang was seeking to commune with Roku, that was the only location with a strong enough spiritual connection to Roku to allow such communication, and only when the jewel embedded in Roku's statue was illuminated by the light of the Winter Solstice sun. Zuko ordered all speed, and with luck he felt they would reach the island either before Aang, or shortly after.
As he caught sight of the sky bison - a good distance away from Fire Nation territorial waters - he swallowed convulsively. He couldn't call on Iroh or Cadence's advice at this point. The former was below, comforting the latter who was still recovering from her hostage experience. He'd have to handle this on his own, and hope he made the right decisions.
"The Avatar is in range!" Lieutenant Jong - the recently promoted troop who'd spotted the wilted vegetation when Cadence had been captured - called out. He was currently manning the telescope as lookout.
Lieutenant Zhin - Jong's recently promoted partner who'd remembered Cadence's effect on plant life - moved to the catapult controls. "Should we open fire, sir?"
Zuko stared up at the speck that the Sky Bison appeared to be to his unaided vision, weighing his options. Finally, he spoke up. "No," he stated finally. "With only the one catapult, there's no way we'll be able to hit him. That Bison moves too fast in the air, and he'll have more than enough time to dodge every shot. Don't waste the ammo."
Feeling a heat from around his neck, he opened the pouch in time for the pink flame to release another scroll. Opening it, he smiled. "Besides, we'll have more than enough ships before too long. My Father's been informed that the Avatar is heading for Crescent Island, and he's put the blockade of our territorial waters under my command."
"I thought Commander Zhao was in charge of the defensive fleet?" another of the troops asked.
Zuko couldn't suppress his smirk. "He is," he replied. "And today, he takes his orders directly from me." He did his best to pretend to ignore his troops' laughter at that.
Seeing the approaching blockade, Zuko went to the catapult. "We're launching a signal flare," he ordered. "Pass the order on to the blockade to use non-explosive ammunition. Since there are ways to learn Airbending without Airbenders, the death of the Avatar will notend his threat. He is to be captured alive, no exceptions."
Lieutenant Zhin nodded as he loaded the appropriate flare signal into the catapult and launched it. Lieutenant Jong was able to confirm that the ships of the blockade - with the exception of Zhao's own ship - were obeying the order and loading nets, grappling hooks, and other such weaponry into their catapults, tied to the ships to draw the captured Avatar back in once the Bison was caught.
Zuko watched as Aang maneuvered his Sky Bison to evade the weapons fire. I was right, he thought to himself. He and his Bison have a very strong bond. In the air, they're all but untouchable. Our best bet to capture him will be on the ground. "Ignore the Avatar," Zuko ordered. "Set course straight for Crescent Island, full speed. Signal five ships to join us as we pass through the blockade. If we manage to get to the island ahead of the Avatar, we can set up an ambush. If not, we'll have enough men to swarm him under if necessary."
As the ship passed through the blockade, Zuko was curious though unsurprised to see that Zhao's ship was one of the ones that turned to join his, even as the Avatar successfully evaded the capture weaponry and make it past the blockade.
While Zuko's plan for capturing the Avatar at Crescent Island was sound, the sheer number of troops he was trying to move through the Temple proved in error. Aang was able to make it into the chamber where Roku's statue was hidden during the confusion, although his two friends, his flying lemur, and his Bison were caught. Since the chamber sealed itself off so it couldn't be opened, Zuko ordered Zhao to arrange the troops around the only entrance, in order to capture Aang when he came out.
Meanwhile, Zuko led his own troops to another part of the temple bordering the chamber, and consulted the Fire Sages who remained loyal to the Fire Lord about the temple's construction, planning a means by which the chamber could be broken open from another wall.
Before he was ready to actually attempt this, however, the doors opened, a blaze of blue light behind them. Zhao gave the order to attack...and Zuko returned with his men just in time to see that Avatar Roku had somehow infused Aang to return to the physical world for a time.
Zuko immediately gave the order to withdraw. He knew they didn't have the manpower to face a fully realized Avatar, and trying to engage now would only waste lives. He had considered using the hostages he'd taken to stop Roku, but his first counterattack freed them. His second unleashed the fury of the volcano the Temple was built on.
As he'd suspected, the manifestation of Roku didn't last long, and the Avatar was exhausted afterwards. Unfortunately, there was no way to take advantage of the situation with how the volcano's eruption was affecting the land and seas, and so he was forced to follow along behind him again.
There was some good news for Zuko, however. Apparently, Avatar Roku had appeared in Iroh's chambers during the sunset specifically to help calm and comfort Cadence. She seemed to be back to her old self now...save for bedding down in the crow's nest.