Vash'jir is the other Cataclysm starting area available, and this is the first WoW zone that takes you under the sea.
There'll be no accusations, just friendly crustaceans.
You begin your journey by answering a call to arms that takes you to your capital city's port, where you are told that you are supplying aid to the war effort for a critical island located off the coast of Stormwind. The Alliance are trying to keep the island, since if the Horde are able to capture it, it will give them a perfect staging location for attacks against Stormwind. Your boat arrives, and you and the other reinforcements ship out.
Your trip is interrupted when your captain spots a wreck nearby, and when you stop to attempt to offer aid, giant tentacles emerge from the sea and consume your boat, dropping you into the water.
As you sink, a naga appears to take you captive, but he is driven off by a shaman's fire and you go unconscious before waking up in the hold of your sunken ship.
The shaman who saved you is named Erunak Stonespeaker, and he is a high-ranking member of the Earthen Ring, a group of shaman who seek to maintain the delicate balance between the elemental forces that make up the world.
The Earthen Ring have come to the underwater domain of Vash'jir because they have sensed a disturbance that might threaten the elemental lord of water, Neptulon, and the naga seem to be the cause of it. Erunak's attunement to the elements grants him the power to put a spell on you that allows you to breath and move quickly underwater, and you immediately set out to rescue your drowning shipmates and supply them with weapons before the naga return. When they do, you and your group are outnumbered and are forced to retreat to an underwater cave.
As you progress through Vash'jir, new caves become available, so you always have a place to rest. Eventually, you are able to tame a seahorse that you can use as an underwater mount.
You fight off naga invaders at your new base, and discover that they have taken up residence inside an ancient underwater demigod named Nespirah.
You go inside Nespirah, and are able to communicate directly with her brain, which tells you that the naga have rendered her powerless and are mining her body for pearls before turning her into a weapon.
You are able to release the naga's hold on her, and she kills them all by activating a self-defense spell.
Elsewhere, your efforts to thin out the naga numbers result in you finding a piece of an ancient weapon in the ruins of Vash'jir.
The Earthen Ring are able to attune your mind to this weapon, and allow you to see through the eyes of the being who wielded it, who turns out to be a fierce battle maiden of the naga from years ago.
You fight through the battle maiden's memories as you experience their past battle to defend Vash'jir from invading vyrkul forces. This allows you to see how powerful the high-ranking naga are, and the almost insurmountable military force they are capable of assembling. With this kind of warfare expertise, Neptulon is in trouble.
You head to the surface to send word to your faction leader, and soon reinforcements arrive, as a giant submarine comes and picks you up to assault the giant creature that shipwrecked you.
You hit the creature, Ozumat, with all the firepower you have, but it is able to escape.
Progressing further, you discover another ancient demigod, L'ghorek, is being attacked from the inside, not by naga, but by the Twilight's Hammer, the cult obsessed with restoring Deathwing to power.
They are using a magi ritual in an attempt to connect him to a unknown powerful creature deep beneath Vash'jir (probably an Old God.) You clean out the cultists and L'ghorek dies, unwilling to be used as a weapon.
Erunak senses that the naga are ready to unleash their full attack on Neptulon's realm, and you and your allies speed toward the Abyssal Maw, the entryway to Neptulon's realm, where the naga forces are fighting water elementals. The naga attack your submarine and destroy it, and all seems lost until Neptulon finally shows up to defend his home.
The naga summon Ozumat back, and the creature attaches itself to Neptulon's head and drags him into the Abyssal Maw as a prisoner, the victorious naga following to lay siege to Neptulon's Throne of Tides. To make matters worse, a giant tentacle emerges from the whirlpool and sucks Erunak down below as well.
You descend into the whirlpool and reemerge in the elemental plane of water, outside the Throne of Tides, Neptulon's realm and one of the first dungeons in Cataclysm.
This dungeon has you attempting to clean out the Throne of naga and drive off Ozumat to rescue Neptulon.
Some corridors are blocked early on, since Ozumat is holding on from the outside.
Lady Naz'jar, one of the high-ranking naga, is the first boss.
After defeating her, you activate a defense mechanism that is installed in the throne that drives Ozumat off temporarily. Making your way down the previously blocked hallways, you first discover Erunak, who is being controlled by a mind parasite.
You must fight him long enough to detach the parasite from his body, and then kill the parasite. Erunak is safe, but he is too weak to help you any further.
Soon you find Neptulon, temporarily free of Ozumat's influence.
The final fight in the dungeon deals with you protecting Neptulon from enemies as his diminished power returns. As soon as it does, however, Ozumat returns, and Neptulon uses his power to make you and your party massive and able to fight him off. Unfortunately, as you do, Ozumat kidnaps Neptulon once again and whisks him off to parts unknown, probably to be seen in a later game patch.