Severus sought his own greatness, his own respect. What does Voldemort have him doing? Listening at keyholes, kneeling, bowing and scraping, serving the glory of Voldemort. This wasn't what he signed on for. He enjoys the power he feels when he had a victim within his grasp, yes. But still, he is a slave, and he has no illusions to the contrary. However, he has seen what happens to those who tried to leave Voldemort's side, and he doesn't relish the idea of being found dead in an otherwise unscathed room while Muggle authorities scratch their heads and try to determine a cause of death. Or, worse, to never be found at all, because Voldemort has made sure there is nothing left to find.
He bides his time, considers his options, and follows his orders. His assignments become more and more irksome to him, as he is told to follow Dumbledore around Hogsmeade whenever the Headmaster comes into the village. With his ear pressed to the door of the room into which he saw Dumbledore disappear, Severus hears a ridiculous woman touting her supposed Seer background and skills. He stifles a sigh. This will be another night spent on worthless spying and, again, he'll have nothing of interest to report to his impatient master. The word rankles with him. That he, Severus Snape, should have a master!
Then, from nowhere, there is a third voice in the room, one that Severus hasn't heard before: The one with the power to vanquish the Dark Lord approaches... born to those who have thrice defied him, born as the seventh month dies...
Suddenly a pair of strong hands grips his shoulders and drags him back from the door demanding to know what he was doing. Severus sputters and says he was lost. The smelly old barkeep laughs and says that doesn't sound very likely. Severus tries to argue, but the old man isn't buying it. He tries to break away from his assailant's grip, but he's caught fast by this infernal old man and flung through the door of the room as he hears, "... as the seventh month dies..." He is face to face with Albus Dumbledore, and he feels his knees go weak. He knows, from his younger years, that Dumbledore is a powerful Legilimens. He quickly blocks his mind and faces his former headmaster, swearing that he was lost. He searches for the third person, the one who made the astonishing claims about the Dark Lord. But there is no one else present. However, he sees a woman with the shawls and spectacles sway a little on her feet and he realizes it was she. She made a prophecy... a prophecy that said...
He must get back to the Dark Lord. This is surely the most important news he can tell him. Perhaps this will finally lift him out of the lowly outer circles of Voldemort's followers, and assure that his days of hiding behind garbage cans and listening at keyholes are over.
Dumbledore looks at him searchingly, and wonders what to do with him. Finally he allows him to leave, much to the consternation of the barman. Snape Apparates straight back to Voldemort and tells him everything.
Voldemort is, indeed, grateful to have this alarming information. He immediately sets out to identify and destroy this child. The child will be born the following summer. Death Eaters are sent to learn where in the wizarding world children are expected to be born at the end of July. It is a huge task, but they ultimately find that the Longbottoms and... no... it can't be... the Potters? James Potter's child could vanquish the Dark Lord? Snape's immediate vindictive glee over the possible destruction of the Potter line is short-lived when he remembers to whom James is married.
An unfamiliar and unwelcome feeling begins to creep into Snape's consciousness, at first fleeting and faint, but growing stronger as days go by: Conscience. The startling green eyes and friendly, non-judgmental attitude of Lily Evans Potter swim in front of him on a daily basis. He begins to gain Voldemort's trust, and to be given more important tasks. But contrary to making him feel better, this change only serves to drive home to him that he lives by the grace of Voldemort, and that if Voldemort decides he is unworthy, he'll be dead. He wants out, but cannot see a way, especially since Dumbledore clearly knew that he was spying.
Why did Dumbledore let him go, anyway? It's hard for Snape to understand. If someone were caught listening to Voldemort through a keyhole, green light would fly quickly and without pause to consider. But Dumbledore let him walk away. Perhaps there would be more freedom after all on Dumbledore's side. But how to make that transition now, when Dumbledore knows he is a spy?
Voldemort determines to kill Lily and James, as well as Frank and Alice Longbottom, before their children are born. Since one of these couples seems to have some magic that might create such a formidable enemy, all four of them must die before their brats come into the world. Severus is slightly sickened. He hasn't yet had to kill anyone he cared about. His nerves begin to get the better of him as he imagines every day that he will hear that Lily is dead.
Three times Voldemort tries to kill the Potters and three times they survive. Three times the Dark Lord also makes attempts on the lives of the Longbottoms and three times they escape. Voldemort is angry and suspicious. It almost seems as though the intended victims have been forewarned and given time to escape. He believes that someone must be leaking information, but who is it?
Back at Hogwarts, Dumbledore is intrigued by the anonymous intelligence that arrives at indefinite intervals and by unconventional means. He is warned, six times, of possible attacks, always pertaining to the Potters and the Longbottoms. Meanwhile, scores of others are hunted down and killed by Voldemort and his followers and no notes of warning appear before these deaths. Who is secretly helping the Potters and the Longbottoms? In each case, Dumbledore is given time to intervene and prevent the planned murders. Yet no one has come forward to claim responsibility for the leak. Though he can be certain of nothing yet, Dumbledore has his suspicions. Nonetheless he does not interfere with the Dark Lord and his followers at this stage. Instead, he bides his time and uses this invaluable information to preserve lives.
Lily is delivered of a boy. Severus so hoped it would be a girl, as the Prophecy definitely spoke of a he. But it is a boy. And those irritating Longbottoms had a boy too. And now, with both babies born and healthy, Voldemort is more determined than ever to eliminate his enemy. In fact, the multiple escapes of the Potters and the Longbottoms have fueled his belief in the Prophecy ("born to those who have thrice defied him..."), and he is determined to discover which boy is the threat and kill him. Perhaps he'll kill both, just to be safe. And, of course, the parents must die too, for causing all of this inconvenience to the Dark Lord. It takes a lot of effort to achieve world domination, and to have to put so much energy into eliminating two couples and their brats is inconceivable. It must be done soon. Snape continues to try to learn the latest plans and to thwart them somehow, without being detected. This is becoming too difficult and too dangerous; to be constantly in the presence of Voldemort and the other Death Eaters... to have to work his Occlumency abilities on a continual basis... And all for James Potter's son and some brat called Longbottom to whom he has no connection whatsoever? He isn't even sure why he's trying to help the Longbottoms, except that they seem connected to Lily somehow, and Snape feels that he must avert the murder of these boys. But it's becoming easier said than done. Every day brings danger and impossible challenges. Staying alive is an increasingly difficult task. Snape feels ready to snap. Something has to change.
As if providence heard his pleas, he is summoned to Voldemort. The Dark Lord tells him that he has determined that the Potter baby is the threat and will be the first target. Snape's insides twist. Voldemort says that Snape must get closer to Dumbledore and obtain the position at Hogwarts that Voldemort never was able to claim. He should gain a professorship, and spy on the Headmaster, and learn more about the Potters' whereabouts and goings on. The multiple escapes have worried Voldemort enough that he fears to strike until he can get inside intelligence from Dumbledore's camp about who is helping the Potters and the Longbottoms. Snape must work out how to get the job, and how to ensure Dumbledore's trust.
Snape is at once elated and perplexed. How to win Dumbledore's trust after the Prophecy? He realizes he has no choice but to try, and that, with Dumbledore, the best strategy will be to tell the truth - or, at least, a great deal of it.
He goes to Dumbledore to seek employment. Dumbledore confronts him directly with the incident at the Hog's Head. Snape opens his mind - or most of it - to Dumbledore, telling him that he was, indeed, in the employ of Voldemort that night. He repeats exactly what he heard, and he admits to telling Voldemort. He tells Dumbledore exactly why he doesn't want to be in the employ of Voldemort - how he has been left to mundane and sometimes degrading duties - nothing more than slavery. He gets rewards and punishments as a wayward child might. He is neither appreciated nor respected. He wants out. He tells Dumbledore that Voldemort has focused on the Potter boy. He tells the Headmaster that he is grieved at the outcome of his mission, and he will do whatever he needs to do to make up for his mistakes. He alludes to the warnings that were anonymously sent, disclosing the Dark Lord's plans against the Potters and the Longbottoms.
Dumbledore considers. It appears that Snape has been helping Dumbledore, by trying to keep both couples safe. But that isn't enough. Snape's change of heart may have come for any number of reasons and may just as easily change back. Even if Snape is sincere in this moment, how can he trust him to keep his word as pressure from Voldemort mounts? He tells Snape that he would like to arrange another interview, to give him time to think things over. When Snape arrives for the second interview, he is met not only by the Headmaster, but also an outraged Lily Potter.
Dumbledore has seen a bit more of Snape's feelings than Snape intended to show him, and has bested his former student by bringing along the one person who can most easily move his conscience. Lily was probably the only person who accepted Snape as he was, without strings or judgment and without any agenda of her own. Now, Dumbledore has told her everything and invited her to help determine the best course to take. James is not present, which is some small relief to Severus. Lily accuses Snape of treachery. He apologizes, and he finds, to his surprise, that he means it. He wants to know what he can do to help.
Dumbledore suggests that he could become a spy for the side of the Order. Snape is wary, but interested. The problem is, says Dumbledore, Voldemort will be on the lookout for such a duplicity, as he has asked Snape to take this very role on his own behalf. Additionally, the allure of the Dark Arts and the possibility of another betrayal must be nullified in some way, so that the Order can, with absolute certainty, trust Snape. They must have a way, a foolproof way, to ensure Snape's purportedly changed loyalties. Lily says that Snape should take the Unbreakable Vow with her. Snape balks. That is a very serious request! Lily counters that his actions against her son warrant extreme measures. Voldemort will now be after Harry every day of his life. Lily will not be satisfied unless Snape takes an Unbreakable Vow to protect her son and be loyal and obedient to Dumbledore's leadership from now on. She further demands that, even if she and James, or even Dumbledore, should die in the fight, Snape will do everything in his power to protect Harry and help his cause, as long as Severus and Harry are both alive.
Now Snape feels trapped. He won't be allowed to leave here unscathed again, if he refuses. At the least, he is sure he'll be turned over to the Ministry as a spy. And he knows what happens to spies. A lifetime stay in Azkaban is not a welcome prospect. Besides, Voldemort sent him here to get a job. If he fails... Snape shudders at the thought. And if he assents... how can he stay alive while spying on Voldemort? And can he really bear being the protector of James Potter's son?
Dumbledore offers to be Lily and Severus' binder. Snape considers. He was looking for a way out from under Voldemort. Voldemort wants him to be a professor at Hogwarts. So, he could convince Voldemort that he is still on his side, and has followed his orders. He asks Dumbledore for the DADA job. Dumbledore counter-offers the Potions position, as Professor Slughorn is retiring. Dumbledore is wary of giving Snape the DADA job, due to the uncertainty of his loyalties at the moment. Besides, Dumbledore has long ago figured out that the DADA job is cursed, and that anyone who takes it will have one year's employment only. He wants Snape safely ensconced at Hogwarts for far longer than one year. Snape thinks about the life he will have, teaching a new generation of brats, and being under Dumbledore's thumb. But, at least Dumbledore doesn't kill people who make mistakes, or expect people to appear before him on their knees. He gives Snape more respect, even now, when Snape is a known enemy, than Voldemort ever did.
Swallowing the bitter pill of aiding James Potter, Snape takes Lily's hand and swears to protect her son, to work for the Order and to obey and be loyal to Dumbledore. Dumbledore binds them and the deal is made.
Snape keeps Dumbledore carefully informed about Voldemort's plans and operations. He works with Dumbledore to choose careful "leaks" to give to the Dark Lord, to convince his master of his loyalty and value. These efforts take some months, while trust and a pattern of duplicity are established. Several months later, Snape learns that Voldemort is ready to go after Harry, and he tells Dumbledore. Dumbledore rushes the Potters into hiding and offers to be their Secret Keeper. They insist on using Sirius. Dumbledore assents, and leaves them to put the Fidelius Charm in place, which is Lily's job - James is a natural at Transfiguration, but Lily is a master at Charms, and has practiced for this moment. Sirius is present and insists that they use Peter. He isn't sure of Lupin's loyalties, and no one would suspect Peter. Sirius can continue to provide cover for Peter by perpetuating the ruse that he is the Secret Keeper. The Charm is cast.
Peter turns into a rat, metaphorically if not literally, and tells Voldemort the location of the Potters. Death Eaters are summoned to Voldemort's side. Snape sends Dumbledore a signal that he is going, races to Hogsmeade, and Apparates to the Dark Lord's side with the other Death Eaters. Voldemort says that he knows the location of the Potters' hiding place. He will go tonight to kill the child. Snape feels his peril and Lily's. How did this happen? Dumbledore said the secret was safe! He suggests to Voldemort that Lily could be very valuable to his cause. Voldemort is unconvinced. After all, he has made three attempts to either kill or control Lily and all have failed. Snape assures him that she is a brilliant potions maker. Voldemort says he has that in Snape. Carefully, Snape pushes Lily's talents, hoping that Voldemort will spare her and he'll be able to summon help in time to prevent Harry's murder. James doesn't enter his mind.
Lily would be valuable in many arenas, says Snape. She has the absolute trust of Albus Dumbledore and the Order. She is an important and popular member of the wizarding world. She could be kept under the Imperius Curse if need be, and used to further the cause. Her extraordinary talent in Charms and her intuitive creativity could prove valuable tools, especially since she is so completely trusted throughout wizarding society. He convinces Voldemort that Lily's ability or knowledge, either in Charms, Potions or some other area, is worth trying to acquire, and they decide that Voldemort will put the Imperius Curse on her in order to ensure her cooperation. Snape knows that he cannot outwardly speak against the killing of the Potter baby without arousing suspicion and anger from the Dark Lord. He and some other Death Eaters, all masked and unknown to each other, are given coordinates for Apparation. As the others disappear, Snape sends a hurried message to Dumbledore with the coordinates and follows his master. It is his hope that Dumbledore will be able to send Order members before the boy is killed, or that there will be some way for Snape himself to intervene and save Lily and Harry.
He lands, a few seconds behind the others, in Godric's Hollow, in front of a modest home. There is light coming from the house, but no one appears to be home. However, the Dark Lord enters while the others wait outside. Then, Snape sees the flashing lights of spells, hears Voldemort's voice, but he appears to be alone - there is no other voice and no one else present. Then he realizes - the Fidelius Charm. The Potters are inside, he just cannot see or hear them. One flash of green... then another... the Death Eaters wait, uncertain what to do, and Snape cannot send another warning for fear of being caught in the act. He cannot imagine that either of the Potters has cast the Killing Curse, and he holds his breath, waiting to see what happens next. A third jet of green light appears and then seems to tear the house apart. The Death Eaters disperse in a panic, as Muggles begin to see the house coming down, and wonder aloud what is happening to it. They all say how fortunate it is that no one is inside. Snape waits where he is, perhaps under a Disillusionment charm. Silence. There are no more curses flying, and most of the others have gone. Snape knows, in his heart, that Lily is dead. He waits for the triumphant Voldemort to emerge from the ruins, but he does not. Carefully, Snape tries to find his way through the ruins. The Fidelius Charm still protects Harry, and Snape can neither see nor retrieve him. He can, however, see the remains of his master in the twisted rubble. Being unable to see Harry (or, possibly, his parents), he is unsure what happened or who, if anyone, remains alive. He is only certain that the Dark Lord is dead. Though Voldemort bragged that he had secrets to defy death, that he was immortal, his mangled body looks very mortal indeed, to Snape. As the other Death Eaters disperse, a rat scuttles out of the ruins and flees into the darkness. Snape could almost swear the animal held a wand between its teeth... Quickly he Apparates to Hogsmeade and sends another message to Dumbledore.