A black sailboat rose and fell with the howling wind and crashing waves, carrying Snape and his companions toward Azkaban.
They stood on the narrow deck as icy, salt-laden seawater splashed up from below, striking their bodies with force.
Seeing this, Dumbledore immediately lifted his wand, conjuring a transparent protective shield that arched above them.
As they advanced, the sky gradually darkened, as though a massive black curtain were slowly descending, blotting out the once-blue heavens.
An unnatural chill and a dense mist swept in from every direction, forcing the three of them to clutch their traveling cloaks tighter around their bodies.
Yet the cold still pressed relentlessly inward. A strange, indescribable wave of negative emotion crept into their hearts like vines growing unseen in the dark.
Snape's body began to tremble uncontrollably. Old memories, bitter, painful ones, were dragged from the depths of his mind by some unseen hand and replayed again and again before him.
Before Dumbledore could act, Snape raised his wand instinctively. "Expecto Patronum!"
A silver-white giant serpent erupted from the tip of his wand.
This time, it was no longer the indistinct phantom it once was. Its solid, gleaming body shimmered with mysterious patterns.
The serpent coiled affectionately around Snape, its forked tongue flicking in and out, hissing softly.
"Oh, so you're a snake," Snape murmured under his breath. "I thought you'd sprout antlers and eagle claws by now."
As the Patronus's glow spread outward, the suffocating cold and despair vanished within its circle of light, and warmth and hope returned to their hearts.
"You can summon a fully formed Patronus, Severus." Dumbledore's eyes were filled with satisfaction as he gazed at the white serpent. "That truly puts my mind at ease, though it is a snake."
"What's wrong with snakes? They're quite adorable in their own way," Snape said, gently stroking the serpent's head.
The sailboat continued to pitch violently on the storm-tossed sea, the water around them darkening ever further.
A bolt of lightning split the pitch-black sky, and raindrops the size of beans began to hammer against the waves.
For an instant, the lightning illuminated the darkness, revealing faint, floating shadows, Dementors hovering over the surface of the sea, exuding their cold, despairing aura.
No one could tell how much time passed before the prison finally came into view: a solitary structure rising from the sea, a place whose name meant "the Realm of Destruction" or "the Abyss of Hell."
It loomed like a slumbering beast, its massive stone walls glistening with a chilling, metallic sheen beneath the lash of the waves.
The boat came to a stop near the shore. Amid the whipping rain and wind, the three of them struggled up onto the rocks.
"Do you think," Snape said after steadying himself, "that a skinny, half-starved dog could swim from here back to the Scottish Highlands?"
"Oh? What an odd question, Severus," Dumbledore replied, flicking his wand to cast several spells to dry and warm them. "Even a perfectly healthy magical dog with three heads would never make it back to shore from here."
"Nothing, Professor." Snape muttered, though a flicker of admiration crossed his mind, for Sirius Black.
After twelve years of imprisonment, Snape could hardly imagine what sort of determination or madness had driven the man to swim across the North Sea to reach Hogwarts.
"There aren't any Ministry guards stationed here?" Snape asked, glancing at the towering walls and the desolate entrance.
"Would you really want some lowly Ministry official to stand watch here for long, Severus?" Moody rasped, tapping his staff against the ground. "Let's get inside."
The three of them stepped into Azkaban.
The interior of the prison was no better than the outside. Water dripped continuously down the damp, grimy walls. The torches mounted there burned with a sickly green flame that gave off no warmth at all.
Many prisoners lay motionless in their cells, completely devoid of life. If not for the faint rise and fall of their chests, Snape would have thought they were already corpses.
Only a few still sat huddled in the darkness, muttering to themselves.
As they passed one cell, Snape suddenly stopped, then quickly stepped backward to look again.
"What is it?" Moody whispered, his tone edged with wariness.
"I know him," Snape said quietly, his expression conflicted.
Inside the cell sat his former dorm-mate, Mulciber.
Mulciber seemed to hear their footsteps. His dull, lifeless eyes moved sluggishly toward the bars, and his cracked lips trembled soundlessly. "Help... me..."
It seemed he hadn't been here for very long, he hadn't yet lost all hope of escape or survival.
"Let's go," Snape said, turning away. "I used to say 'sure, sure, sure' whenever someone asked me for help, but then I'd always forget to actually help them.
"That's really not good, you know. Now, if someone asks me again, unless I truly care enough to want to help, I'll just say, 'Sorry, I don't want to,' and walk away.
"For someone like me, who tends to please others too much, that's my way of practicing honesty and courage."
"Mr. Snape," Dumbledore said softly, leaning close, "I know a spell that can silence people. Why don't you teach me yours? I'd very much like to try it right now."
"I'll shut up immediately, Professor." Snape mimed zipping his lips shut with his fingers.
At that moment, a sightless Dementor drifted past them. It seemed to sense the faint trace of happiness emanating from their group, a rare thing within these walls. It glided toward them.
Before Snape could react, the silver serpent coiled around his body suddenly reared up and shot forward like lightning.
It encircled the Dementor, forming a tight, glowing cage around it.
Dark smoke hissed from the Dementor's body. Though it made no sound, the three of them could almost see its silent scream of agony.
Within moments, all that remained was a filthy black cloak on the floor. The Dementor itself had vanished completely.
"Professor," Snape said in astonishment, "I thought Dementors couldn't be destroyed."
"I believe," Dumbledore replied in a low voice, "that perhaps the light of your Patronus is like the dawn breaking in the East, its power may surpass ordinary limits."
"Then you must be the setting sun in the West, Professor," Snape retorted, rolling his eyes. He stooped, gathered up the discarded cloak distastefully, and continued onward.
"There she is," Snape said finally, pointing to a cell where a frail, withered house-elf sat slumped in the corner. "I think that's Hokey."