Castle Defense links the story of TW1 and TW2. It is download only content that was released in 'levels' and dose not require a copy of Two Worlds II to play. The 'levels' were released in order as follows and can only be played with the Two Worlds II: Castle Defense download.
Arenas: Training elite imperial soldiers isn't easy. It requires years of preparation and practice. When ready, recruits are taken to their final test by Emperor Gandohar himself. Only those who survive are deemed worthy of being called Imperial Elites. Source: The Publisher Website.
Level 2: While Emperor Gandohar defends Oswaroth against the onslaught, he commissions his top general Sordahon to lead a group of his choice soldiers behind the enemy lines. The objective is to destroy the main Orc camp, cutting off their primary source of reinforcements. Direct orders from Gandohar state not to allow a single Orc to retreat from the battlefield. Source: The Publisher Website.
Level 3: The annihilation of the Orc armies was but a stepping stone in Gandohar's search for unlimited power. Imprisoning the fire god Aziraal in the woman Kyra could grant him such hideous strength, but would require sustaining her life unnaturally. This can only be achieved by channeling another being's lifeforce energy into her using the ancient artifacts known as Maliel's Thrones. While searching the desert Gandohar has come under attack from the temple's guardians. Protect the Emperor from these vicious monsters! Source: The Publisher Website.
Level 4: Gandohar dispatched the temple guardians at the surface. Meanwhile, Sordahon's expedition into the catacombs under the temple was proving fruitful, having successfully located the first of Maliel's Thrones. The mission is still far from complete, however - by desecrating the temple catacombs, Sordahon has awakened the true guardians of the Throne. Defend Sordahon and the treasure from the monster's aggression! Source: The Publisher Website.
Level 5: One of the Emperor's search parties found the second Maliel's Throne in a burial ground on Elkronas Island. While the unit's commanding officer was forwarding word to Gandohar of the discovery, one of his soldiers accidentally touched the artifact. Within seconds, the entire unit was surrounded by undead. Fend off the flesh-eaters until Gandohar arrives with reinforcements. Source: The Publisher Website.