HP:Brewing The Half-Blood Prince

The Professor kneels in the dark.
[1v1 / Obsessive Devotion / Reverse Domination / Hurt & Comfort / Healing / Absolute HE (Happy Ending)]
No wands drawn. No Dark Lord summoning him through the Mark on his arm.
Just the damp, familiar cold of his private laboratory, and the soft, deliberate footsteps of the boy he pulled out of St. Mungo's.
Severus Snape thought he understood poison. He thought he knew cruelty.
When Albus Dumbledore dumped an emaciated, magic-drained orphan at his threshold, Severus treated the boy like any other volatile reagent-kept in the shadows, fed with indifference, and permitted only to tend fires and stir cauldrons through the dead of night.
Lucas Graham was supposed to be harmless.
A quiet stray with bowed shoulders and respectful eyes. An apprentice whose hands never shook, whose compliance never wavered, and who stayed awake until dawn just to brew beside his master.
Severus believed he was in control.
He was wrong.
He didn't notice when the taste of his morning tea subtly shifted.
He didn't notice when the ancient dungeon wards ceased responding to his own blood.
And he certainly didn't realize that the complex alchemical formula the boy had been transcribing for months wasn't a scholarly thesis-
It was an exclusivity report. A slow-acting, irreversible cage designed for exactly one person.
"You taught me how to extract every hidden impurity, Professor," the apprentice murmurs, stepping out of the shadows with a gentle, terrifying smile. "Did you truly think I would leave your heart untouched?"
The lock turns from the inside.
The master becomes the ingredient.
And Severus must finally learn what happens when the stray you fed turns out to be a starving predator.