The Lord of the Rings Online: Helm's Deep is the fifth expansion for the MMORPG The Lord of the Rings Online. It was released on November 20, 2013, after it was postponed by two days from the original release date, due to a power outage. The expansion is available for download both on the web and on Steam. The Battle at Helm's Deep is created in-game using refined technologies that Turbine created during the development of the expansion, which allow for a significantly larger amount of action and character models during a session. The new expansion increases the in-games level cap to 95, and one of the main new features is the ability to fight "epic"-scale battles such as the Battle of Helm's Deep. The expansion also adds modified trait trees and five new zones to explore in Western Rohan.

In Helm's Deep, Turbine chose to provide a more lore-accurate portrayal of the Battle of Helm's Deep from Tolkien's work, as opposed to the film adaption by Peter Jackson, where some details were modified or omitted. As a result of this, several important events that occurred in the books but did not make it to the film are depicted in-game, such as clashes at Helm's Dike in front of the fortress, and the Glittering Caves of Aglarond.

Storyline Helm's Deep concludes the storyline that began shortly after the Siege of Mirkwood expansion and continued in the Rise of Isengard and Riders of Rohan.

Volume III: Allies of the King Book 11 - The Golden Hall As the refugees of the city of Byre Tor prepare to leave their temporary cave shelter, the player and his travelling companions decide that the news of Saruman's atrocities in Wildermore must be reported to King Theoden despite the penalty for breaking their banishment. To avoid angering him even further with the presence of a Dunlending woman, Nona and the Elf Corudan escort the refuges to the nearest surviving city of Forlaw, while the Rohirrim men Horn and Gleowine together with the player ride to Edoras. Their timing turns out to be most fortunate, as they seek audience just after Gandalf has arrived and woken the King from a long slumber. Éomer is released from imprisonment, Grima Wormtongue is thrown out of the court and after a short preparation, King Theoden musters his army to ride forth and meet the forces of Isengard head-on. Gandalf, Aragorn, Legolas, Gimli, Eomer and Gleowine depart with the King's riders while the player and Horn stay behind in Edoras to assist Lady Eowyn, who has been ordered by her uncle to bring both citizens of Edoras and the refugees from other corners on Rohan into the safety of Dunharrow.

Book 12 - War in the Westemnet After making arrangements for bringing a large number of civilians to Dunharrow, the player and Horn fulfill the promise given earlier to Eomer by visiting his home town of Aldburg and confirming that his regent manages to lead the people in his absence. They are caught up with by Nona and Corudan and the whole party returns to Edoras. Before Eowyn and the refugees can depart, it is revealed that a servant of Wormtongue remained undiscovered in the city and is now actively engaging in both sabotage and murder. Before the spy can be apprehended, he flees Edoras and the player's party sets out to chase him through the lands of Westemnet, which are now besieged by the White Hand forces. After conversing with Thane Herubrand of Woodhurst and his son Herefara, they learn that a war band of Dunlendings bearing the sign of a Talon of the Falcon has been seen marauding in the area. Both the player and Nona desire revenge on the Falcon Clan, which had betrayed their Ranger friends to Saruman in Dunland. Before they can act however, a more urgent message arrives: the Fords of Isen have fallen to the enemy, their defenders Elfhelm, Grimbold and Erkenbrand are nowhere to be found, a massive army from Isengard marches through the Westfold and King Theoden's forces have taken refuge at Helm's Deep. The party splits once more: Nona is unwilling to abandon her quest for vengeance and Horn is unwilling to leave her, so they set out to track the Falcon clan, while the player and Corudan ride to Helm's Deep. On their way they meet Gandalf the White, who advised the King to turn his army to Helm's Deep and now is seeking far and wide for the survivors of the second battle of the Fords of Isen. After Gandalf finds Elfhelm's eored, Elfhelm relays to him the recent news: the force that came from Isengard was many thousands strong and Erkenbrand and his men were driven south of the Fords, beyond the river Isen. Seeing their situation hopeless, Elfhelm chose to retreat and, despite Grimbold's protests, took his men back into Rohan before Saruman's army poured through the Fords in their wake. Gandalf orders Elfhelm to protect Edoras, which now sits empty, and travels to the Fords to find Grimbold. His men almost all dead, Grimbold refuses to abandon the Fords, where Prince Theodred now lays buried. Gandalf helps him reconnect with Erkenbrand and leads the combined force to Helm's Deep.

Book 13 - Helm's Deep The player manages to arrive to Helm's Deep just before the gates are closed in preparations for the battle. Erkenbrand, the military commander of Hornburg, took most of the defenders and weapons with him to the Fords, so the King's army can only supplement itself with refugee villagers and makeshift weapons. As the night falls, the White Hand forces begin to arrive and Gamling the Old holds them for a short while at Helm's Dike, before being overwhelmed and retreating into the fortress. Orcs, Uruks and Dunlendings assault the Deeping Wall and the defenders led by Aragorn manage to hold them off, until a section of the wall is blown and the enemy pours into the Deeping Comb. Eomer, Gimli and the player are trapped in the Glittering Caves and have to protect the refugees hidden there. Their plan to lead the refugees away through the secret mountain tunnels fails when it is revealed that those passages are already known to the enemy - a group of Dunlendings emerges in the caves from a direction though safe and is led by Lhue Brenin, the Chieftain of the Falcon clan. With Gimli's help, the player manages to slay him and exact vengeance upon the Dunedain slain in Tal Methedras. As the dawn comes, Theoden chooses to ride forth with the remaining able riders and meet the enemy head-on. The sound of the Horn of Helm Hammerhand shatters the morale of Saruman's minions, as Theoden, Legolas and Aragorn cut through their ranks. It is then that Gandalf arrives, with Grimbold and Erkenbrand leading a combined force of footmen and riders. The Dunlendings surrender en-masse and the Orcs and Uruks try to flee into Westfold, only to be trapped by the arrival of Huorns from the Fangorn Forest. In the aftermath of the battle, fallen are counted in many numbers, but the White Hand army is destroyed and Rohan still stands.

Book 14 - The Breaking of Isengard King Theoden, Eomer, Gandalf, Aragorn, Legolas, Gimli and the player set out for Isengard. As they approach the Gap of Rohan, they are met by Halbarad and the remaining Rangers of the Grey Company, their long ride to the aid of their chieftain Aragorn complete at last (this is the first time where the Epic storyline contradicts the Lord of the Rings books, as the Rangers are not supposed to meet Aragorn until after visiting Isengard). At the gates of the now flooded Isengard, the company finds Peregrin and Merdiadoc. The Hobbits relay the tale of their escape from Saruman's Uruks, meeting with Treebeard, the Entmoot and the march of the Ents on Isengard. Gandalf, Theoden and Aragorn set out to confront Saruman, while the Rangers begin to search for their kinsman Lothrandir, who has been imprisoned in Isengard since the Falcon Clan's betrayal in Dunland. In a section of the wall that escaped destruction by the Ents but is quickly being flooded, the Rangers begin opening prison cells until they finally discover a man in the signature Grey Company outfit. To their horror, the rescued prisoner is completely broken in body and mind alike: his face is mutilated beyond recognition and his shallow eyes do not seem to recognize his friends. He only manages to utter a single word before collapsing and dying, a broken shadow of the strong-willed man Lothrandir once was. However, while mourning their fallen friend, the Rangers discover that it was not Lothrandir underneath the garbs. Despite using the magic to torture his body and mind in horrific ways, Saruman failed to break the Dunadan and in an act of corrupted twisted cruelty had him switch garbs with a prisoner from Dunland. Continuing the search, the player finally finds Lothrandir in another cell - beaten, bruised and weakened, but very much alive and sane. At the same time, Gandalf breaks Saruman's staff and casts him out the Order of the Wizards and the White Council. Treebeard promises to keep watch over the Wizard now trapped in his tower, while Pippin briefly comes in contact with the Palantír thrown out by Grima Wormtongue. Aragorn is much rejoiced over both finding his captured kinsman alive and ending Saruman's threat to Rohan and extends his thanks to all of his allies: the Fellowship, the Dunedain, the Rohirrim and the player alike.

Book 14 is the end for the "Volume III: Allies of the King" storyline. The next major storyline: "Volume IV: The Strength of Sauron" began in March 2015.

New zones The Helm's Deep expansion adds the in-game region of Western Rohan, sub-divided into Broadacres, Stonedeans, the Kingstead, the Westfold and the Eastfold, with the major settlements including Edoras, Aldburg, Dunharrow and the fortress of the Hornburg. The regions of West Rohan are depicted during the invasion Isengard's forces during the War of the Ring in the prelude to the Battle of Helm's Deep, and many settlements have been destroyed in their onslaught. Many of the more minor features of Rohan which played little part in the books and were omitted from the movies altogether appear in the expansion, such as the Púkel-Men that line the road to Dunharrow. The new regions create a new landscape link between the lands of Eriador and Rhovanion for the first time since the Mines of Moria expansion in 2008.

Broadacres The Broadacres are under assault by the Warg riders of Saruman, and catastrophe looms as the flames encroach on the Riders' settlements. In the north, the village of Torsbury is assaulted by Dunlendings, pressing their invasion out of the Stonedeans. A flat and fertile land of rich soil and swaying, grey-green grass, growing so high in places that it reaches the knees of a man on horseback. The land is among the least rocky in the Mark, and while a few chestnuts and elms dot the landscape, most of it is treeless. The Broadacres is ruled by Fríthild, the sole female Reeve in the Mark. A shield-maiden by birth and training, she was the only child of the former knight, Fríthgist, who raised her like a son. When Éowyn visited Edoras as a child, Fríthild treated her like a foster-sister. Ever since, Éowyn has wanted to follow her footsteps and wield a sword in battle.

Stonedeans The men of Dunland, with help from Saruman's Orcs and Uruk-hai, control a great deal of the Stonedeans. They prepare to cross the river-gorge at Brockbridge, where a few brave men hold back an endless tide threatening to wash over northern Stonedeans. A region among the foothills of the Misty Mountains, the Stonedeans consists of crags, broken stones, tall oaks and firs, and rushing rivers. A source of many of the metals worked by the Rohirrim, particularly iron mined from the low mountains that surround Nan Curunír. This Riding among all others in Rohan is the most similar to Dunland. Historically poor and uncivilized compared with the remainder of the Westemnet, the Stonedeans have seen many marriages between Eorlingas the Dunlendings. Rohirrim from more prosperous lands even call it "Deanland" in jest.

Kingstead