Now having to focus on the battle before him, Voldemort had to move quickly to shield himself.
"You cannot hope to defeat me, Black!" he called back, behind his shield.
Sirius rapidly cast a strong shield breaker and followed it up with another cutter before he paused and called back, "You keep thinking that Riddle, you half blood bastard!"
Yet more curses and charms flew between the two before Riddle call-demanded, "Do not call me by that filthy... muggle... NAME!"
More curses and protection charms, with Sirius moving about as if he was almost dancing. His moves, though appearing slow due to how smooth and graceful they looked, were actually quite quick. He was needing to shield and spell-swat dark curses and charms aside a lot less than Voldemort; who saw dodging as a sign of magical weakness.
Suddenly Sirius saw, out of the corner of his eye, the now one-armed centaur detach itself from the fountain and gallop towards him.
'Dumbledore,' he thought. A hesitation between casting curses at Riddle and he cast a Blasting Hex at the centaur, blowing it to smithers.
"Stay out of it, Dumbledore!" he roared. "I told you, Riddle is mine!"
However, Dumbledore proceeded to ignore Sirius and was walking forward; his eyes again focused on Riddle.
"It was foolish to come here tonight, Tom," said Dumbledore calmly. "The Aurors are on their way―"
"By which time I shall be gone and you, dead!" spat Voldemort. He sent another Killing Curse at Dumbledore, but missed; instead, hitting the security guards deskbehind the old man, which burst into flame.
Dumbledore flicked his own wand and Voldemort was forced to, once again, conjure a shining silver shield out of thin air to deflect it. The spell, whatever it was, caused no visible damage to the shield, though a deep, gong-like note reverberated from it. An oddly chilling sound.
"You do not seek to kill me, Dumbledore?" called Voldemort, his scarlet eyes narrowed over the top of the shield. "Above such brutality, are―"
He had to shut up and again start defending himself from Black's attacks. Sirius had only hesitated for a few moments in annoyance that Dumbledore had, once again, interfered.
"We both know that there are other ways of destroying a man, Tom," Dumbledore said calmly, continuing to walk toward Voldemort as though he had not a fear in the world, as though nothing had happened to interrupt his stroll up the hall. "Merely taking your life would not satisfy me, I admit―"
"There is nothing worse than death, Dumbledore!" snarled Voldemort, incantlessly defending himself from Sirius's attacks. "Merlin, damn it, Black!" he roared. "I'm trying to hold a civil conversation with Dumbledore!"
"I do not care, you snake-faced freak!" Sirius snarled back. "Just ignore the old man. He's a worthless sack of shit, anyway!"
Dumbledore, once more, began casting at Riddle/Voldemort - obviously not appreciating the idea he should simply be ignored - while Sirius returned to his attack. Seeing magic cast at him from two different directions at pretty much the same time, Voldemort vanished. There was a burst of flame in mid-air above Dumbledore just as Voldemort reappeared, standing on the plinth in the middle of the pool where so recently the five statues had stood.
One more jet of green light had flown at Dumbledore from Voldemort's wand, just as Fawkes swooped down in front of Dumbledore, opened his beak wide and swallowed the light whole. He burst into flame and fell to the floor, small, wrinkled and flightless.
At the same moment, Dumbledore brandished his wand in one, long, fluid movement; the water in the pool rose up and covered Voldemort like a cocoon of molten glass.
For a few seconds Voldemort was visible only as a dark, rippling, faceless figure, shimmering and indistinct upon the plinth, clearly struggling to throw off the suffocating mass. Then he was gone and the water fell with a crash back into its pool, slopping wildly over the sides, drenching the polished floor.
"MASTER!" screamed Bellatrix.
With the opportunity presented to him, Sirius spun towards LeStrange and cast a dark purple curse at her. Not expecting it she soundlessly collapsed to the ground either unconscious or dead.
Thinking it might be over, that Voldemort had decided to flee, Sirius made to step out from behind his significantly damaged marble wall, but Dumbledore bellowed, "Stay where you are, Sirius!"
For the first time, Dumbledore sounded frightened; though Sirius could not see why. The hall was quite empty but for themselves, the 'unconscious' Bellatrix still trapped under her statue and the tiny baby Fawkes croaking feebly on the floor. Suddenly Voldemort reappeared standing next to Bellatrix and looking down at her.
Sirius immediately began casting again.
Voldemort looked up and, with a look of fury at Sirius, returned to his own attack. Both combatants, ignored Dumbledore.
"You've killed her!" Voldemort practically screamed at Sirius. "You've killed my Bella!"
"You'll be joining her in a few moments!" Sirius snarled back. "Just accept it! You're a dead man who doesn't know when to stay dead!" And he began slinging curses, hexes and everything he had at the man.
Voldemort returned like for like, but had resorted to the darkest of curses in his anger.
Sirius dodged them all and yelled, "Give up you half-blood, muggle-raised, slit-eyed, noseless freak and just accept it!"
Riddle increased his attack, but so did Sirius. "Lord, my arse!" yelled Sirius between casts. "Voldemort, my arse! French for 'Flight from Death' is accurate enough! Coward!"
Having caught something from the side of his eye, Riddle gave a small start of shock.
Suddenly, he cast up a massive crystalline shield and, from behind it, snarled, "I'll be back, Black! I shall personally kill you for this affront!" Then he bent down, reached to LeStrange with his off-hand, latched onto her robes and side-along apparated with her out and away.
Sirius looked around to see if the snake-faced mongrel was going to put in another appearance. However, instead of spotting him again, saw that the other end of the Atrium was full of people. The floor, covered in water from the fountain in many places, was reflecting emerald-green flames that had burst into life in all the fireplaces along one wall; and a stream of witches and wizards was emerging from them. As Dumbledore walked forward from the other side of the smashed fountain, Sirius saw the tiny gold statues of the house-elf and the goblin leading a stunned-looking Cornelius Fudge forward.