2 days before the events of Chapters 1 and 2...
Lord Voldemort was confused. He couldn't believe it, but he was. A couple of months back he started hearing voices in his head, stuff like "The night draws close…" and "Look to the Highlands, there you will find me!" At first he thought it was some form of curse or jinx, but when he had tried every form of magic that might stop the voices, he began to worry. Heeding the advice given to him by the voices he had immediately Apparated to a place he knew not far from Hogwarts.
When he arrived at the destination he immediately realised something was wrong, there were two voices here, arguing, apparently, with each other. "You can never pass the gates of Hogwarts while I am here! My theoretical magic has paid off, hasn't it! If I hadn't researched the Soul shield, I'd be helpless!" said a new voice, a beautiful, melodic voice, yet it had a slightly big-headedness about it.
"Shut up, girl, you cannot withstand against me AND my kin for long! Ah, he draws close. Come, Tom, I am inside the Shrieking Shack!" said the first voice.
Sudden realisation struck Voldemort, the voice was his noble ancestor, Salazar Slytherin!
The Shack was as cold and inhospitable as Voldemort remembered from his school days, yet he immediately began reaching out with his mind, searching for Slytherin. He finally found him in the attic. As there was no way into the house from the outside, he was forced to Apparate into the attic. There he found a huge sword, the hilt made of frosted, hardened emerald, and a blade of some green metal. Along the side was the inscription: Made by Merlin, Wielded by Salazar. Voldemort knew what it was, a Horcrux, and he knew what to do. "I, Lord Voldemort pledge my life, body and soul to Salazar Slytherin so he may use my body as his physical form until such a time as another body shall become available.".
"That is acceptable." said Salazar.
Voldemort shone with a green aura, then he was possessed, sharing a body with Salazar. Salazar mind began to work, thinking what his next options would be. Of course his eventual aims would be to conquer the Wizarding World, but he would need a Head Quarters or Fortress. Hogwarts! But he would need a small army to take over Hogwarts, what with all the teachers and students there. Then one of Voldemort's ideas came swimming to the surface: Death Eaters!
It took two days to assemble an assault force worthy of the historic school. 500 Death Eaters, 50 Dementors and 80 or so Inferi. The assault force, disguised with disillusionment charms, was waiting outside the gates for the go-ahead signal when Salazar/Voldemort felt a mental twinge. Rowena was free! They felt a sudden surge of anger and vented their frustration on the Hogwarts wall, which after being frozen, cracked and burnt more times than imaginable collapsed in a heap. "GO! AND THE ONE WHO RETURNS WITH RAVENCLAWS WAND WILL BE PROMOTED TO SECOND IN COMMAND!" they roared, the voice of Tom Riddle and the rasping one of Salazar Slytherin oddly merged.
The assault on Hogwarts had begun.