Indeed. HoMM6 plot is told not very well in-game. Not to mention that some things were retconned in DLCs, 50SoP and in MMX.
OK, here is "quick" summary of HoMM6 story line, SPOILERS
All begins during Ancient Age when Angels, after defetaing and scattering Demons through far corners of Ashan, launched crusades against Faceless. This conflict not only nearly wiped out both races but also destroyed Shantiri Empire - vast kingdom of all Elder Races: Humans, Elves, Dwarves, Nagas, Angels and Faceless. During fights leader of Angels, archangel Michael, was slain by Faceless Master Assassin Erebos. Michael's and his brother Uriel's mother also died during this ambush. This war, known as Elders Wars, ended when Sar-Elam, wizard and ascended Seventh Dragon, forced both sides to sign peace treaty. Erebos was against this idea but he was imprisoned by his brothers in Tomb of Thousand Terrors.
Angels were nearly excinted so archangels Sarah and Uriel plotted a plan to avoid this. They used angels Hall of Memories to gather and store souls of killed angels in hope to find new bodies for them in the future. They also forged seven swords and gave them to human dukes of Falcon Empire. Swords have one task to do: prepere royal bloodlines as vessels for fallen angels.
In year 520 YSD duke Pavel Griffin dies fighting demon Ahribban summoned by orc shaman Torghul. His soul is saved by his sister Svetlana, but before she could do anything, Pavel's body (and soul in it) is taken by angels. They use it to bring back to live archangel Michael. Pavel's son, young Slava, became new duke and his aunt Sveltana became regent until he is mature.
In year 564 YSD duke Gerhart Wolf invade Griffin Duchy to force out friendly Orc tribe from Holy Empire. Fight between Gerhart and Slava is stopped by Uriel and emperor Liam Falcon. Archangel forced Slava to gave his eldest daughter Irina as wife to Gerhart.
Slava is not happy but he can't object "emperor" decision. During wedding night Irina harm Gerhart when he tried to rape her. She is imprisoned after that.
Slava and his three other children, Anton, Kiril and Anastasya (Sandor left Empire earlier, angry for his father lack of guts to protect Irina), went to Emperor Court to persuade Liam to release Irina. Uriel has on his mind much more important metters so he mind-control Anastasya to kill Slava.
Second Blood Moon Eclipse begins.
Sarah used Kiril as a pawn and trade his soul to enter demon prison-dimension Sheogh and for free passage to demons Dragon God - Urgash. She is trying to heal him from his eternal agony but instead is wounded by him and turned into half-angel, half-demon. This event starts Second Eclipse three years earlier before it should be. If Second Eclipse would start in three years, Blind Brothers predicated that forces of light would fall, so Sarah and Uriel tried to change that.
Sarah used Urgash's claw from her body (it stuck there, when he wound her) to create Blade of Binding and to use it and Kiril (now with demonic Prince of Destruction in him) to destroy Faceless Invisible Library. With this weapons angels could once and for all destroy Faceless. Kiril would vanish after destruction of Library or become Faceless himself if he choose to help Faceless. He chose to use third option and bring Invisible Library to Sheogh.
Meanwhile Anastasya is executed by her brother Anton and bring to un-life by her great aunt Svetlana. She discover that her mentor Uriel used her as a pawn in order to bring angerl Aurora to life - his and Michael's mother. She is quickly "cured" from love to her menor, when she discover that truth. Anastasya went to inner mind of Uriel, when she confronts him, defeats him and in result destroys hismind. Uriel's body is destroyed by demons along with emperor Liam and his guards. These demons, lead by archdemon Ahribban, are defeated by Anton. Ahribban is sealed in magical artifact by Michael, so he couldn't back to Sheogh.
Second Eclipse is ended but fight continue. While Uriel is dead and Sarah abandon angels plan and stay with Kiril in Sheogh, Michael want to launch an attack to Faceless hidden temples in Abyss deep under Ashan surface. Griffin children with their mother Cate attacks instead angels sky city, where Hall of Memories is located. They want to stop Michael before new Elders Wars starts with all its horrors and magic so powerful, that probably would destroy Ashan itself.
When Griffins enter the Hall, Cate starts seven-day ritual to send all trapped and tormented angel souls to their Dragon God - Elrath, whey they belongs. Michael appears when ritual is nearly completed and is defeated by Griffins. He and Cate both dies and threat of new Elders Wars is stopped.
This is end of H6 and so-called Uriel's Deception
. This is however not the end of Elders Wars leftovers. MMX tells a story of Faceless Master Assassin Erebos and explain some questions from H6. Also H6:50 Shades of Purple
also ties some loose ends of H6 plot.
If anyone wonders WHY Cate died, here is explanation sent to my by Marzhin, when I asked him about it. It was planned to be in game, but for some reasons it was skipped in final product:
“Subdued and chained, Michael is brought into the Hall of Memories where your mother, Cate, the Dragon Knight of Malassa, is finishing her week-long ritual to free the souls of the angels killed during the Elder Wars. Hundreds of burning golden orbs are circling around her while she levitates in the center of the room, entranced. The last name she utters is Michael’s name, before calling Elrath himself, demanding the release of his children, allowing them to move on to a new life. As the final word is spoken, a pillar of burning light descends from the heavens and hits the center of the room in a blinding explosion. The soul embers whirl around the column as Elrath accepts your mother’s plea.
Michael himself, having accepted the judgment of his Dragon God, lowers his head before being dissolved into golden dust from which two golden fires emerge – one of which you know belongs to your own grandfather, Duke Pavel, the vessel Uriel and Sarah used to bring Michael back. But as your gaze returns to your mother who has become the epicenter of the maelstrom, you discover with horror that the Dragon Knight herself is being disintegrated by Elrath’s light. You realize she always knew a servant of Malassa could never survive such an ordeal – this was a price she was always willing to pay, the ultimate sacrifice. Her own soul ascends last and maybe it’s only wishful thinking on your part, but you could swear to have caught a glimpse of your father’s spirit, waiting for her. Then the pillar of light dissolves, and the noise of endless wars is silenced, at last.”
Sorry for spelling.