Harry was tempted to just go with, just hop on the broomstick with Bellatrix and the snake. Chances were that they would get out safely. And if they did get out safely, and Harry came with, then he and Professor Quirrell could go back in time and look perfectly innocent, everything could go back to normal.
If Harry stayed behind and turned himself in... then even if everyone assumed Harry had been a hostage, assumed Harry had lied to Professor McGonagall's Patronus at wandpoint... even if Harry himself got off lightly, well...
It wasn't likely that the Defense Professor would go on teaching at Hogwarts.
Professor Quirrell would have reached the predestined end of his career, in February of the school year.
And yes, Professor McGonagall would kill Harry, and yes, it would be slow and painful.
But staying behind was the sensible, safe, sane thing to do, and Harry was feeling more relaxed than regretful.
Harry turned to Bellatrix; he opened his mouth to instruct her a final time -
And there was a hiss, a weak hiss, a hiss that sounded slow and confused, and the hiss said,
"What wass... that noisse?"
Through the corridor the old wizard strode. He came to a metal door and opened it, already knowing from memory that the cells within were empty.
Seven mighty and discerning incantations the wizard spoke then, before he moved on; it would be little enough exertion in total, with so few cells left to check.
"Teacher," Harry hissed. So many emotions bubbling up in him, all at once. He knew, though he could not see, that the green snake around Bellatrix's shoulders, was slowly lifting its head to look around. "Are you... all right, teacher? "
"Teacher?" came the weak, confused hiss. "Where iss thiss?
"Prisson," Harry hissed, "the prisson with life-eaterss, we were to resscue a woman, you and I. You tried to sslay the protector man, I blocked your killing cursse, there was a ressonance between uss... you fell unconssciouss, I had to defeat the protector man mysself... my guardian Charm wass disspelled, the life-eaterss could tell the protectorss that the woman had esscaped. There iss ssomeone here who can ssensse my guardian Charm, probably the sschoolmasster... so had to disspell my guardian Charm, find different way to hide you and the woman from life-eaterss without guardian Charm, learn to protect mysself without guardian Charm, sscare off life-eaterss without guardian Charm, then devisse new esscape plan for you and the woman, and finally, cut hole in thick metal wall of prisson even though I am only firsst-year sstudent. No time to explain, you musst go now. If we never meet again, teacher, then I was glad to know you for a time, even though you are probably evil. It iss good to have the chance to ssay thiss much: Goodbye."
And Harry took the broomstick and presented it to Bellatrix, saying simply, "Get on."
He had decided to keep the memories. For one thing, they were important. For another, he and the Defense Professor had started planning this a week ago, and Harry wasn't about to obliterate the whole last week, or explain to Bellatrix exactly what needed to be Obliviated. Harry could probably fool Veritaserum, and if Dumbledore insisted that Harry drop his Occlumency shields for a deeper examination... well, Harry had acted heroically throughout.
"Sstop!" said the snake. Its voice was stronger now. "Sstop, sstop, sstop! What do you mean, goodbye?"
"Esscape plan iss rissky," said Harry. "My life iss not at sstake, only yourss and herss. Sso I am sstaying, turning mysself in -"
"No!" said the snake. The hiss was forceful. "Musst not! Not permitted!"
Bellatrix mounted the broomstick; Harry could sense (but never see) her head turning to look at him, she said no word. Awaiting him, perhaps, or merely awaiting his orders.
"No longer trusst you," Harry said simply. "Not ssince you tried to sslay the protector man."
And the snake hissed, "I did not sseek to sslay the protector man! Are you fool, boy? Sslaying him would not make ssensse, evil or no!"
The Earth ceased to turn on its axis, paused in its orbit around the Sun.
The snake's hiss was now more furious than anything Harry had ever heard from the human Professor Quirrell. "Sslay him? Had I ssought to sslay him he would have been dead within ssecondss, fool boy, he wass no match for me! I ssought to ssubdue, to dominate, force him to drop sshieldss upon hiss mind, needed to read him, to know who awaited hiss reply, learn detailss for memory sspell -"
"You casst killing cursse!"
"Knew he would dodge!"
"Wass hiss life worth sso little? What if he did not dodge?"
"Would have pusshed him out of the way with own magic, fool boy!"
Again the pause in the planet's spin. Harry hadn't thought of that.
"Witlesss dunce of a plotter," hissed the snake, so angrily that the hisses seemed to overlap and slither over each other's tails, "clever imbecile, cunning idiot, fool of an untrained Sslytherin, your missplaced misstrust hass ruined -"
"Thiss iss not a fair time to argue," Harry observed mildly. The surge of relief trying to flood through him was canceled by the increased tension. "Ssince I cannot get angry at you properly, without opening mysself to life-eaterss. Musst russh, ssomeone may have heard noisse -"
"Explain esscape plan," the snake said imperiously. "Sswiftly! "
