"Avada Kedavra!"
Oleandra darted to the side, narrowly avoiding the green beam of light, then pirouetted to evade the second beam concealed within the bright glare of the first. Even though she had expected Daphne to lead with Voldemort's signature Killing Curse, being on the receiving end of such a spell never failed to send shivers down her spine.
The ability to use the Killing Curse was not a matter of talent; it was purely a question of magical strength and murderous intent. To single-mindedly set oneself upon taking another's life was not something easily done, so for Voldemort to use Killing Curses as readily as Oleandra could snap her fingers was indicative of the sheer depth of hatred he bore for this world and everyone in it.
"Don't you know any other spells?" Oleandra said as the pages of the Book of the Stars rifled rapidly of their own accord before her. "Some Dark Lady you are!"
Unfortunately for her, Lord Voldemort was not so easily taunted. Oleandra was forced to hop back several times in quick succession as a flurry of green beams came flying at her. Most were parried by Excalibur of its own accord, while the rest shattered the flagstones of the dungeon floor at her feet, pelting her with showers of rock fragments. The terrain was not to her advantage; there was nowhere to take cover from the Killing Curses here.
"Thursaz!" Oleandra shouted, curling her fingers in the shape of the thorn rune.
Oleandra did not expect such a feeble attack to land, and, as predicted, Daphne easily parried her spell with a flick of her wand. Still, her objective had been accomplished, and she had managed to buy herself a moment's breathing room. She waved her wand, extinguishing the fires burning in the wall-mounted braziers and plunging the corridor into complete darkness.
"Avada Kedavra!"
Excalibur pivoted in mid-air, repelling the curse and sending it back whence it had come, briefly illuminating Daphne's grim face and bathing it in a baleful green glow. Oleandra glanced up at the sword floating above her, which showered her in golden light… it was highlighting her presence in the darkness, but perhaps she might yet turn this fact to her advantage…
"What have you done with the cup?" Daphne asked coldly, breaking the silence as the duel lulled to a halt. "I didn't see it on you."
While Daphne was concerned about the Horcrux's whereabouts, she was at present more worried with the golden blade floating above Oleandra's head. After seeing the damage it had wrought in Draco Malfoy's hands, she had attempted to draw it from the floor where it had embedded itself, but to no avail. No matter which spell she used, it would not budge, nor could she blast away the stone in which it had taken root.
Even now, Daphne ceaselessly muttered incantations under her breath while she waited for Oleandra to respond, yet still she couldn't bind the golden the sword to her will, or, at the very least, separate it from its mistress! If it hadn't been for that sword, she would have killed her at least ten times already…
"I'll tell you if you beat me,"Oleandra replied in no uncertain terms.
"Then I'll simply make you wish you were dead, then kill you," Daphne replied coldly. "Crucio!"
As though drawn by an invisible magnet hidden within Oleandra's pockets, crimson lightning crackled from Daphne's wand and streaked towards her, completely ignoring Excalibur even as it moved to shield her. The lightning jumped from its blade, arcing towards her…
"Tinne!" Oleandra shouted, invoking the holly-tree rune.
A scream escaped Oleandra's lips as the Cruciatus Curse set her nerves aflame, despite the rune's protection. Somehow, even though her body felt as though it were being raked with white-hot blades, she managed to leap back, breaking the connection and forcibly ending the spell from her end.
"The Elder Wand…!"
That, Oleandra realised, was what had empowered Daphne's Cruciatus Curse to such a ridiculous degree.
She hadn't noticed the amplification earlier, since the Killing Curse would have killed her regardless of whether it was enhanced and she had managed to avoid being hit thus far, but now she would have to be doubly careful of the other spells Daphne cast, since they would be in a league of their own!
No matter what, she had to put some distance between them!
"Suit!"
The dark, leathery extremities of the Lethifold's fabric-like body shot out from Oleandra's back like a cloak billowing in the wind as it dragged her backwards. Excalibur flew off in pursuit as she streaked away like a meteor towards the intersection in the corridors behind them, and they both disappeared behind a corner.
Daphne strode forwards at a leisurely pace. She knew this was a fight Oleandra would not back down from, so she felt no concern that she might flee. This was Dumbledore's faction's last stand, so if she ran away with her tail between her legs, not only would she lose her only chance to save her sister, but she would lose all her allies as well…
"Playing hide-and-go-seek, are we?" Daphne said mirthlessly. "If this is your idea of an ambush…"
A faint, golden light emanated from the corridor on Daphne's right as she approached the intersection. This was obviously a trap; even an idiot would have noticed the glow spilling around the corner.
Daphne nonverbally cast a Human-Presence-Revealing Spell, obtaining the information that there was indeed a human other than herself nearby… but strangely enough, rather than revealing Oleandra's exact position, the spell could return nothing more than the vague assurance that she was not alone… despite the fact that she was using the Elder Wand.
Daphne brought her wand arm down, flinging a twelve-foot-long boa constrictor from the tip of her wand through the intersection, and a dark shadow swooped down from the corridor on the left, wrapping around the boa and smothering it as it screeched and writhed helplessly.
She frowned… this couldn't be the extent of Oleandra's trap, could it? She waved her wand again, this time casting a nonverbal Revealing Charm.
"This…!"
Daphne's pupils shrank to pinpricks as golden marks in the shape of footsteps drew themselves across the floor before her, leading into the corridor on the right… and a second set that traced a wide arc around the corner, looping back behind her!
She whirled around in the nick of time, the Shield Charm's incantation already cast in her mind.
With a flick of her wand, Daphne repelled Oleandra's Stunning Curse, sending it streaking back into her chest. Oleandra's one eye rolled back into her head, her mouth forming a small, surprised 'o' as she crumpled into a heap on the floor as Harry's silvery Invisibility Cloak cascaded to her feet.