Ironic, Severus thought, that even a snake could be a sheep;
more so, to find a lion the shepherd. A good shepherd, even.
Albus would not abandon the flock for a lost sheep,
one who had been drawn away by another crook,
but nor would he leave off trying to bring the lost child home.
While most of the flock dozed those ten years, Albus
had remained alert, searching, coaxing Severus back
through the cold, misty thickets of Azkaban and hate
with promises of a warm, peaceful hearth at Hogwarts.
At last Severus, finding himself weary and heavy
with the pricking brambles of his conscience, returned to the fold.
Once a sheep, always a sheep, he thought.

He loved Albus for taking him in, loved him for being
a better master than Voldemort had been. Still he knew -
even the good shepherd is also the butcher.
How many of the other poor lambs had trusted Albus
without knowing this or even wanting to,
Severus sneered,
had put their heads in his hands, closed their eyes,
offering themselves to the knife? Caradoc, Benjy,
Edgar, Dorcas - even Lily and that blasted Potter.

The litany was familiar; sometimes he thought
he could hear the quick thuds of the club
as Albus' plans did their work. More than once, lately,
Severus had seen the speculative light in Albus' eyes
turn towards him. But with lithe words and nimble mind
he turned it away, hid himself among the solid facts
of his usefulness and buried the fear in his heart
under the proud barbs of his typical vitriol.

Like a sheep, Severus thought, for now I live
my life in clover, secretly watching
for the moment Albus decides I should be
a sacrifice, a little lamb to the slaughter.

He swore a vow to himself, before and above
the other vows he'd taken, swore that the day
Albus finally sought to bind him to that purpose
he would be more than a sheep, more than a snake.
Yes, I will buck like a ram and bite like a wolf.
Though it may be famous blood I taste,
I will break loose! I will race under the open skies,
back to solitude, my true flock, back to what is
mine, though it be but stubbled grass and mud.