Katara details the events that occur while Aang is unconscious.
Katara writes in her diary about the hopelessness she has felt since the Earth Kingdom fell into the hands of the Fire Nation upon the capture of Ba Sing Se. Having retreated from Chameleon Bay with the fleet of Water Tribe ships, she acknowledges that without Aang, who has been unconscious since Azula shot him with lightning, their future is bleak. Her worry is at its peak when she realizes that without faith in herself and her own abilities, she could never expect to awaken Aang.
Earth KingKuei and his bear Bosco enjoyed their stay with the crew despite their crushing loss before leaving to travel the world on their own. Katara also writes that although Kuei and Bosco left, Pipsqueak and The Duke joined shortly afterward. However, Hakoda was not spurred in their efforts to invade the Fire Nation with these new recruits. With things falling apart at the seams, Sokka did not let his father give up on the invasion plan, which had apparently become the world's only hope.
Back in her diary, Katara recounts how an enemy scout ship had approached their fleet and that they had needed to think of a way to survive, fast. Sokka eventually came up with the idea that they should switch boats with the Fire Nation scout ship as a disguise, making it look like they were on the Fire Nation's side. After demolishing their own ships and escaping on canoes, the crew sailed away from the wreckage; it now appeared as though the Water Tribe fleet had already been defeated.
When the enemies arrived at the remains of the Water Tribe ships, they took credit for the fleet's destruction. Next, Katara writes, came the easy part of Sokka's plan: the Water Tribe warriors invaded the Fire Nation scouter. Although Katara had believed she should have stayed with Aang and was not very willing to fight, it turned out that she did not have to do much; the crew that manned the ship was mediocre. In her diary, she writes, in uncharacteristic optimism for her current state of mind, that she still cannot believe they managed to prevail. The final step of Sokka's plan was to disguise themselves in the crew's Fire Nation garb and continue their voyage, this time on the stolen vessel.
Although having wished to cut through the Serpent's Pass in order to cross into Fire Nation waters from the Earth Kingdom without causing a fuss, Sokka did not anticipate a barricade at the passageway. Hakoda managed to trick the sentry atop the barricade into thinking that they were rendezvousing with a fleet at the other side, but in doing so, the gang discovered that the Fire Nation believed Aang was dead. Sokka's immediate idea was that this misconception could turn in their favor. Katara explains in her diary that since the enemy does not suspect the Avatar and his friends to be causing any more trouble, they can secretly reside in the mainland as disguised soldiers without being scrutinized. All she can do now is have hope that soon, having gotten through all the trials they have faced before, the Avatar will return.
Toph sarcastically jabs Sokka by saying, "You're not gonna tell that pentapox story again, are you?" while he was brainstorming for a way to evade capture by the Fire Nation scout ship. This is a reference to the episode "Return to Omashu", wherein Sokka tricked the opponent officials into believing that Omashu's citizens had caught a dangerous disease called pentapox.
Katara is already showing signs of animosity toward her father, which will become more prevalent in "The Awakening".
In the comic, the Southern Water Tribe ships are destroyed when Team Avatar and the others capture Fire Nation ships to use as a disguise, but in "The Day of Black Sun", the same Water Tribe ships are used again to transport the invasion force.
The plot of "The Bridge" takes place concurrently with the events of Escape from the Spirit World, which follows Aang while he is unconscious, and "Going Home Again", which follows the fate of Zuko and Azula after the fall of Ba Sing Se.
As there is no mention or sight of a bridge at any point throughout the comic, it can be reasonably assumed that "The Bridge" was named for the fact that it bridges Books Two and Three.