The Dealaam Rift
A dangerous clan of dark templar rise, who were followers of Ulrezaj, try to seperate Nerazim from Dealaam and enslave them. The leader of clan posses enormous void and shadow energies that never seen before, superior than even Tassadar.
They hate both Matriarch and Hierarch, and try to assasinate Matriarch first, in order to claim their leader as the true leader of Nerazim.
The clan think that the Khalai has to pay for their crimes had committed on Nerazim in the past. Banishment from their homeworld Aiur, and being hunted one by one like disgusting animals by their brethren.
In addition to sad historical events, The Dark Templar is well aware that Khalai refugees had brought Shakuras into edge of oblivion by bringing Zerg with them, and caused the death of hundreds of Nerazim people.
Hierarch Artanis played a major role in destruction of planet Shakuras, The Dark Templar knows how to use that against the Hierarch, and deceive the people of Nerazim, and pull them to his manages to spread hatret of Khalai, reasoning the destruction of Shakuras.
In the past the clan had tried to assasinate Matriach Raszagal; the clan's leader, the Dark Templar had been stopped by Zeratul, their leader was prentice of Zeratul, thats why the Dark Prelate had had mercy on young dark templar, not executed him right there but, put him in custody. Some members of the group had managed to escape.
The Hatret upon Dealaam consumes the Dark as same as Amon consumed the Khala..
Amon mentions Ma'lash about a mighty Dark Templar that could bring ruin their enemies, even if they loose the war against Ouros, the Dark templar would help them rise again, willingly or not. The Fallen X'el Naga feels the hatret he posses. Followers of Amon now considers The Dark Templar as the "Chosen One" by the Amon. The Fallen X'el Naga points out the place of custody of The Dark Templar, thus Ma'lash sends BloodHunters in order to sneak into the jail and save the Dark Templar.
A Trump Card that is merged with oblivion in the end, which was from flesh, blood and psionics; yet another one is rising from void and shadows which is fresh and ready to be used... Clashing armies and penetrating defences(Kerrigan), or sneaking and executing from inside(The Dark Templar)...2 ways, 2 different aims.
Fall of Zeratul by Amon serves this goal as well. The Dark Templar somehow senses the death of Zeratul and understands that his time of rise will come too soon.
During the second war, by the absance of Zeratul and the pursuit of survival of the Protoss race, with a little help, The Dark Templar manages to escape from custody, after escape, he hides into shadows, manages to grow his forces secretly, because of pursuit of the Second Great War and the assault on the place of costudy, noone hears about the unexpected escape of him, he is able to know who is entering the void(dying or stealthing) or strenghten void energy, from great distances. He senses the void energies of his comrades, finds and makes them join his cause again.
The Ma'lash's forces during the Second Great War, support The Dark Templar. He recruits Blood Hunters from Tal'darim. Bloodhunters request to make the Shadow Walk, but the leader doesnt allow them thinks that the servants of Amon are not worthy of it, they are nothing but a tool for achieving his clan's goal of ovethrowing Matriarch.
After The Second Great War ended, the remnants of Ma'lash's forces think that after they divide Dealaam and Nerazim and start a civil war, it be easier to conquer and cleanse them once and for all. They made him promise of helping them overthrowing Alarak, just after he claimed his place as the Hierarch of the Nerazim.(Remnants of Ma'lash regard him as chosen one, so his promise is valid for them.)
In the perspective of The Dark Templar, the Tal'darim has to be destroyed because of their worship of Amon, along with the Zerg Swarm. He thinks that it is easier to destroy the authority which is trusting you rather than which is in suspicion.(comparison between the Remnants of Ma'lash and Alarak)
Zagara wants to help and involve in, in order to keep her promise to Queen of Blades about the peace, however Artanis rejects it and tells that this is a "Protoss matter". (Reference to death of Aldaris)
Highlord and Hierarch try to get rid of this threat.
And maybe a love story between a male dark templar and a female scientist terran can be taken as sub-story.
Or a love story between dark templar and a high templar can be taken as sub-story instead.
Terran is neutral for him.
There are thesis-antithesis situations here between Ouros and Amon in terms of chosen was the chosen one of Ouros, she wield psionic powers, she led an army, unified the Char Zerg with Primal Zerg, she became the primal zerg, she and her race were dominant since the begining;
On the other hand Amon's chosen one wields void and shadow energies, always acted alone or with a small group of assasins, he and his people hide and lurk in the shadows, he always wanted to seperate Khalai and Nerazim, he never wanted Khalai to be seperated from Khala like Nerazim. When Kerrigan's race was conquering the planets one by one, the Nerazim were living an exile life away from their ancient homeland.
However, as in common in the begining, even if she contradicts him sometimes, Kerrigan couldn't seperate her will from Overmind; and the dark templar was imprisoned by Zeratul for a long time, so they both had to bow their masters.