In one of the earlier drafts of my mock-up main quest, they player character would be a victim of the Thalmor's mind conditioning, just as some assume Ulfric Stormcloak may have been. After the ship carrying them was attacked by a Sea Leviathan, they awaken briefly on the beach, seeing two robed silhouettes standing over them, they faces obscured by shadow. One of them says something akin to "This one will do." before reaching down, a spell activating in their hand. The player character then blacks out and awakens back in the same spot, clutching a sealed scroll in their right hand, addressed to the Imperial Ambassador. With this, the main quest begins in earnest with the player character seeking out the Imperial Ambassador, delivering the scroll and being recruited by said Ambassador to help in the investigation of House Lariat. All through the first act, the player character encounters a mysterious Altmer, seemingly feeding them vital information and influencing their choices. After following a series of leads, the Ambassador is murdered and the player character is framed for the murder, nightblades in service to Clan Direnni aid in their escape and spirit them away to the Isle of Balfiera. The Castellan of Balfiera was secretly aiding the Ambassador in his investigation and now seeks to bring House Lariat to justice.
However, before any of this can be done, the player character's name must be cleared. To do this, they must acquire evidence of House Lariat's crimes against the Empire, evidence stored in Llugwych Castle, the former headquarters of the Blades in High Rock. The Ambassador's key to the vault there was stolen, but fortunately the Castellan has his own key. And so, the player character, with a nightblade to assist them, depart for Llugwych Castle, while avoiding capture. After entering the castle and braving the many traps still left over from its time as the headquarters of the Blades, they confront the Ambassador's killer, eliminate him and access the vault. There they find evidence incriminating House Lariat, as well as several other noble houses and high-ranking members of the Imperial Legion. After returning to Balfiera with the evidence, the Castellan congratulates the player character, only for the mysterious Altmer to appear once more, seemingly invisible to all but the player character, compelling the player character to kill the Castellan. Knife in hand, ready to strike, the player character manages to restrain themselves and warn the Castellan, which proceeds to knock them out with magic. They then awaken, Clan Direnni's healers having banished the Thalmor's mind conditioning. The Castellan promises them revenge.
The evidence would be taken to a person of great importance, either one of the few non-corrupt Imperial Legion officers or even the Penitus Oculatus, to clear their name and continue the investigation unencumbered. Though they would still have to deal with bounty hunters hired by House Lariat, continuing to pursue them regardless. After being freed from the Thalmor's mind conditioning, several new quests would be made available, such as seeking out Thalmor spies on Balfiera, eliminating agents reaching out the the Wrothgar Orc clans and even confronting the mysterious Altmer in the flesh. The Thalmor's endgame was to wipe out Clan Direnni and allow House Lariat to plunge the province into war, paving the way for an invasion.