This story contains an extract from Harry Potter and the Deathly Hallows, chapter 33: The Prince's Tale
"Come to my office tonight, Severus, at eleven, and you shall not complain that I have no confidence in you..."
They were back in Dumbledore's office, the windows dark, and Fawkes sat silent as Snape sat quite still, as Dumbledore walked around him, talking.
"Harry must not know- neither can Daisy, not until the last moment, not until it is necessary, otherwise how could he have the strength to do what must be done?"
"But what must he do?"
"That is between Harry, Daisy and me. Now listen closely, Severus. There will come a time- after my death- do not argue, do not interrupt! There will come a time when Lord Voldemort will seem to fear for the life of his snake."
"For Nagini?" Snape looked astonished.
"Precisely. If there comes a time when Lord Voldemort stops sending that snake forth to do his bidding, but keeps it safe beside him under magical protection, then, I think, it will be safe to tell the twins."
"Tell them what?"
Dumbledore took a deep breath and closed his eyes.
"Tell them that on the night Lord Voldemort tried to kill them, when Lily cast her own life between them as a shield, the Killing Curse rebounded upon Lord Voldemort, and a fragment of Voldemort's soul was blasted apart from the whole, and latched itself onto the closest living soul left in that collapsed building. Part of Lord Voldemort lives inside Harry, and it is that which gives him the power of speech with snakes, Daisy, hers from their familial bond, and a connection with Lord Voldemort's mind that he has never understood. And while that fragment of soul, unmissed by Voldemort, remains attached to and protected by Harry, Lord Voldemort cannot die."
Harry and Daisy seemed to be watching the two men from one end of a long tunnel, they were so far away from him, their voices echoing strangely in his ears.
"So the boy...the boy must die?" asked Snape quite calmly.
"And Voldemort himself must do it, Severus. That is essential."
Another long silence. Then Snape said, "I thought...all those years...that we were protecting them for her. For Lily. What would even happen to Daisy?"
"We have protected him because it has been essential to teach him, to raise him, to let him try his strength," said Dumbledore, his eyes still tight shut. "Meanwhile, the connection between them grows ever stronger, a parasitic growth. Sometimes I have thought he suspects it himself. If I know him, he will have arranged matters so that when he does set out to meet his death, it will truly mean the end of Voldemort."
Dumbledore opened his eyes, "I know not what will happen to his sister, they are almost one being. Perhaps she would die simultaneously, maybe her magic would die with Harry. Maybe she will live on, as though everything was normal." Snape looked horrified.
"You have kept them alive so that he can die at the right moment?"
"Don't be shocked, Severus. How many men and women have you watched die?"
"Lately, only those whom I could not save," said Snape. He stood up. "You have used me."
"Meaning?"
"I have spied for you and lied for you, put myself in mortal danger for you. Everything was supposed to be to keep Lily Potter's children safe. Now you tell me you have been raising her son like a pig for slaughter-"
"But this is touching, Severus," said Dumbledore seriously. "Have you grown to care for the boy, after all?"
"For him?" shouted Snape. "Expecto Patronum!"
From the tip of his wand burst the silver doe. She landed on the office floor, bounded once across the office, and soared out of the window. Dumbledore watched her fly away, and as her silvery glow faded he turned back to Snape, and his eyes were full of tears.
"After all this time?"
"Always," said Snape.
And the scene shifted. Now, the two saw Snape talking to the portrait of Dumbledore behind his desk.
"You will have to give Voldemort the correct date of the twin's departure from his aunt and uncle's," said Dumbledore. "Not to do so will raise suspicion, when Voldemort believes you so well informed. However, you must plant the idea of decoys; that, I think, ought to ensure Harry and Daisy's safety. Try Confunding Mundungus Fletcher. And Severus, if you are forced to take part in the chase, be sure to act your part convincingly...I am counting upon you to remain in Lord Voldemort's good books as long as possible, or Hogwarts will be left to the mercy of the Carrows..."
Now Snape was head to head with Mundungus in an unfamiliar tavern, Mundungus's face looking curiously blank, Snape frowning in concentration.
"You will suggest to the Order of the Phoenix," Snape murmured, "that they use decoys. Polyjuice Potion. Identical Potters. It's the only thing that might work. You will forget that I have suggested this. You will present it as your own idea. You understand?"
"I understand," murmured Mundungus, his eyes unfocused...
Now the siblings were flying alongside Snape on a broomstick through a clear dark night: He was accompanied by other hodded Death Eaters, and ahead were Lupin and a Harry who was really George... A Death Eater moved ahead of Snape and raised his wand, pointing it directly at Lupin's back.
"Sectumsempra!" shouted Snape.
But the spell, intended for the Death Eater's wand hand, missed and hit George instead-
And next, Snape was kneeling in Sirius's old bedroom. Tears were dripping from the end of his hooked nose as he read the old letter from Lily. The second page carried only a few words: could ever have been friends with Gellert Grindelwald. I think her mind's going, personally!
Lots of love, Lily
Snape took the page bearing Lily's signature, and her love, and tucked it inside his robes. Then he ripped in two the photograph he was also holding, so that he kept the part from which Lily laughed, throwing the portion showing James and Harry back onto the floor, under the chest of drawers...
And now Snape stood again in the headmaster's study as Phineas Nigellus came hurrying into his portrait.
"Headmaster! They are camping in the Forest of Dean! The Mudblood-"
"Do not use that word!"
"-the Granger girl, then, mentioned the place as she opened her bag and I heard her!"
"Good. Very good!" cried the portrait of Dumbledore behind the headmaster's chair. "Now, Severus, the sword! Do not forget that it must be taken under conditions of need and valor- and he must not know that you give it! If Voldemort should read Harry's mind and see you acting for him-"
"I know," said Snape curtly. He approached the portrait of Dumbledore and pulled at its side. It swung forward, revealing a hidden cavity behind it from which he took the sword of Gryffindor.
"And you still aren't going to tell me why it's so important to give the elder Potter the sword?" said Snape as he swung a traveling cloak over his robes.
"No, I don't think so," said Dumbledore's portrait. "He will know what to do with it. And Severus, be very careful, they may not take kindly to your appearance after George Weasley's mishap-"
Snape turned at the door.
"Don't worry, Dumbledore," he said coolly. "I have a plan..."
And Snape left the room. Harry and Daisy rose up out of the Pensieve, and moments later they lay on the carpeted floor in exactly the same rooms Snape might just have closed the door.
Seconds passed, then minutes as the twin Potters sat in contemplative silence, realising everything that they had never known about the potions master they had once thought to be a vengeful creature. Upon seeing the memories of their mother, Daisy now understood that his encouragment and stares had been whistfulness and guilt, not the morbid fascination that her friends had convinced her of.
The red haired twin turned to look at her grim, looking brother. With his shaggy, sweaty hair plastered over his forehead and his eyes downcast he looked exactly like their father had. Not a difference to be seen from this angle. Harry looked up to make eye contact. Tired emeralds stared at tear stained ones and one of many understandings passed between them; possibly their last.
Daisy shuffled onto her knees and scooted towards him. They embraced each other as if they were reuniting after months apart.
"It's okay," Daisy whispered, "It's okay. We'll be alright."
Slowly they moved so only their foreheads were touching and their eyes were open once more.
"I won't stop you," She assured, putting Harry's mind at ease, "I won't go after you. But I want you to promise me something in return."
Daisy's brother smiled up at her, "Anything." He swore.
"Say Hello for me." Daisy said, "Say hello to Sirius and Remus and Mum and Dad for me. I want them to know I love them. Tonks and Colin too. And Fred... oh god Fred, tell him I forgive him for saving me."
She let a little sob escape her lips at the thought of her dead boyfriend. The man who's last moments had been spent reconciling with family and proposing to her, only to be cut off by a wall burying him. The twin swallowed her despair,
"But most of all I want you to tell them thank you. Thank you to Remus for helping me through my first break up and teaching us to defend ourselves. Thank you to Sirius for being my dad when James couldn't be, I'm not even mad that he scared Seamus off before he could ask me out." She let out a weak laugh, "And tell mum and dad thank you for giving me my brother. My brilliant, brave, big brother." The two twins clasped hands, "And my best friend."
He blinked up at her with a bittersweet smile, "Forever and Always?"
"Forever and always."
As a last attempt to cheer his sister up he asked, "What's my payment for being the messenger?"
She chuckled thickly, "You say hello for me, tell them everything; and I'll live for you."
Harry nodded acceptingly and let her sit down again. As he stood up, he gave her one last hug, kissed her on the forehead and whispered,
"I love you my little Snitch."
He walked to the door, paused, and kept going. Down the stairs and to his death.
Daisy Potter clutched at her knees, burying her head in them as she sobbed. Her position did nothing to stiffle the cries that were heard all throughout Hogwarts and her grounds. Both her brother and her knew, if Harry had turned around, he would never have left.