Chapter 2 of Harry Potter and the Half-Blood Prince: Spinner's End
Two cloaked figures Apparate alongside a dark, dirty river. Narcissa Malfoy and her sister, Bellatrix Lestrange, head for a dilapidated brick row house on Spinner's End. While walking, Bellatrix is apparently trying to dissuade Narcissa from doing something. At the house, they are greeted by Severus Snape, who assures them that they are alone, except for Wormtail (Peter Pettigrew). Snape orders Wormtail to fetch drinks for himself and his guests. Wormtail complies while protesting that he is not Snape's servant. Narcissa believes only Snape can help her, but before she says more, Snape points his wand at a concealed door and sends Wormtail, who is listening from behind, scurrying. Bellatrix, distrusting Snape, interrogates him about where (and with whom) his true loyalties lie. Before responding, Snape asks in turn: does Bellatrix really think that the Dark Lord had not asked him those same questions? Does she think he would be sitting there, talking to her if he hadn't been able to provide The Dark Lord with satisfactory answers? Does she think he could have fooled the Dark Lord, possibly the greatest Legilimens in the world?
Snape then addresses Bellatrix's concerns: when the Dark Lord fell, he was at Hogwarts, where Voldemort had ordered him to spy on Dumbledore. He did not hunt for the Dark Lord after his fall for the same reason many other Death Eaters failed to: he believed the Dark Lord was finished. Bellatrix retorts that she searched for him, prompting Snape to sarcastically remark how "useful" she was in Azkaban prison, while he collected sixteen years' worth of information on Dumbledore for Voldemort. Snape continues that he did not stand between the Dark Lord and the Philosopher's Stone; he thought Quirrell wanted it for himself and he acted to prevent that. He failed to respond to the Dark Lord's summons when Voldemort returned so that Dumbledore would continue to believe Snape was still his ally, rather than the other way around. Bellatrix claims she is Voldemort's most trusted lieutenant and would know of any information Snape passed to him. Snape asks if she still retains this status after the Ministry fiasco. On the Dark Lord's orders, he stayed away from the battle to protect his position at Hogwarts. The information Snape supplied made Emmeline Vance and Sirius Black's deaths possible, and the Dark Lord was satisfied with his information. Snape has not killed Harry Potter because it was only Dumbledore who was keeping Snape effective as a spy and out of Azkaban. Killing Potter would have lost him that protection, and he would be unable to help Voldemort. It is Dumbledore's continued trust in him that makes him so useful to the Dark Lord.
With Bellatrix's worries seemingly appeased, Narcissa explains her visit. Voldemort has assigned her son Draco a difficult and probably deadly task. Narcissa wants Snape to protect him. Snape replies that even though he knows about this, he is powerless to interfere, nor will he try. Narcissa believes Draco was assigned this task as revenge for her husband Lucius' failure at the Ministry. Snape admits that the Dark Lord is angry at Lucius. Snape is finally persuaded to swear an 'Unbreakable Vow' to protect Draco and complete his mission should he fail.
Dumbledore's belief in Snape's loyalty has been established in Harry Potter and the Order of the Phoenix, but evidence here indicates he could be a traitor, as he agrees to Narcissa Malfoy's Unbreakable Vow, making Harry's adamant (and lone) belief that he is still a Death Eater seems validated. Snape, whose fidelity to Voldemort is questioned by many Death Eaters, including Bellatrix Lestrange, knows he can help dispel these doubts by swearing a magically binding oath to protect Draco, even at peril to his own life. Bellatrix probably remains skeptical, despite Snape's seemingly convincing answers to her probing interrogation; indeed, it seems that Snape's true allegiance always remains just vague enough to keep each side guessing. Dumbledore, we remember, has always steadfastly defended Snape's loyalty, despite Harry's continuing suspicions. However, readers know that Snape has been acting as a double agent, and this may be a situation where he is forced into taking the vow to maintain his cover. To do otherwise would cast even more suspicion on his supposed loyalties. It is also conceivable that Snape is loyal only to himself, maintaining a tenuous and dangerous position where he can align himself with either winning side.
Wormtail's loyalty is far less questionable, as he is fully dependent on Voldemort for his very survival. Unlike Snape, he is unable to align himself in any way to Harry, Dumbledore, and their allies. And while it initially may seem that Snape has Wormtail under his constant, watchful eye, it is possible that Wormtail is secretly keeping tabs on Snape for Voldemort. Even though it appears that Snape has convinced Voldemort that he is his faithful servant, the Dark Lord probably has lingering suspicions about him or wants to reassure his doubtful followers. However, Voldemort may know by now that Wormtail owes Harry Potter a life debt, an obligation as magically binding as Snape's Unbreakable Vow, and could be a severe liability to the Dark Lord. Voldemort is likely having Snape and Wormtail watch each other.
Rowling also sheds light on some Death Eaters' personal relationships, as evidenced when sisters Bellatrix Lestrange and Narcissa Malfoy affectionately refer to each other as "Bella" and "Cissy." This is a contrast to how Harry has viewed most Death Eaters. Until now, Voldemort's followers have generally been portrayed as two-dimensionally evil characters who unwaveringly serve Lord Voldemort. Other than the Malfoys, little is known about Death Eaters' family life, social interactions, or what factors, other than "pure-blood" beliefs, motivates them. Bellatrix, in particular, has been portrayed as purely evil, fanatical, and probably unbalanced, even by Death Eater standards, and she may believe Voldemort is doing too little to rid impurities from the Wizarding world. In this chapter, however, she is seen as caring about her sister, Narcissa, wanting to protect her from Voldemort.
And while Bellatrix generally remains two-dimensional, the cold and haughty Narcissa, desperate to protect her husband and son, now displays love, fear, empathy, and sadness—emotions not generally associated with Voldemort's affiliates, but that help develop her into a more fully-rounded character. Narcissa believes Voldemort has tasked Draco with a near-impossible mission (in which he will likely fail and then be killed) only as a means to punish her husband, Lucius Malfoy, for his failure to retrieve the Trelawney prophecy at the Department of Mysteries (in Harry Potter and the Order of the Phoenix), and also apparently for Voldemort's diary being destroyed (in Harry Potter and the Chamber of Secrets). This could ultimately affect Narcissa's loyalty to the Dark Lord and also to her sister. And despite their seeming affection for one another, it should be remembered that both Bellatrix and Narcissa readily disowned their sister, Andromeda, as a blood traitor for marrying the Muggle-born wizard, Ted Tonks. (Nymphadora Tonks is their daughter, and thus niece to Bellatrix and Narcissa.)
In Harry Potter and the Goblet of Fire, Snape was sent on an unexplained mission. In this chapter, we learn that his mission was to rejoin Voldemort and pledge his allegiance. At this point we can see, even if Harry has not recognized it yet, that when Voldemort, on his return, spoke of his faithful servant at Hogwarts, he was not referring to Snape but to Barty Crouch, and the one he fears has left him forever would most likely have been Snape, as the one who had run away would have been Karkaroff.
- What might happen if Voldemort learns that Snape has made an Unbreakable Vow with Narcissa?
- What does Narcissa believe is the real reason Voldemort assigned Draco a nearly-impossible task? Is she correct?
- What is Snape's explanation about why he never killed Harry Potter, even though he had many opportunities to do so? Is his explanation plausible? Why?
Further Study 
- Why does Snape make an Unbreakable Vow with Narcissa Malfoy, a vow that puts his own life at risk? Will he tell Dumbledore about it?
- Considering how much doubt there is about Snape's true loyalties, why does Narcissa choose him to protect Draco?
- Why did Narcissa and Bellatrix disown their sister, Andromeda? Can they trust each other? Explain.
- Why does Bellatrix remain suspicious of Snape? Does he convince her that he is loyal to Voldemort?
- Why do Death Eaters remain loyal to Voldemort, despite his tendency to threaten or eliminate even his most devoted followers or their families?
- Compare and contrast evidence that Snape is loyal to either Dumbledore, Voldemort, or even to no one.
- Why might Peter Pettigrew be at Snape's house? Does Snape trust him? Does Pettigrew suspect Snape might be a traitor? Who might Voldemort trust more?
Greater Picture 
As a side note, although it seems that Bellatrix is satisfied by Snape's answers, she could have insisted on him taking Veritaserum (truth serum) before interrogating him. However, she does not, possibly because, as Dumbledore will suggest later, even Veritaserum can be circumvented if it is expected. Though this is nowhere mentioned in the book, it is likely that those who know Occlumency can also cheat Veritaserum, if only by being able to perceive intent to administer the potion. And for that matter, Snape as Potions Master likely has an antidote to Veritaserum brewed, and may have it with him. Dumbledore will not go into detail about the means of subverting Veritaserum; however, Snape is more likely than most wizards to be aware of them. It is likely, though, that Veritaserum would not have helped Bellatrix in this case, if she had asked the questions that we see her asking. Snape's answers are, in every case, the truth, though perhaps not the full truth.
We will find out near Christmas, at the Slug Club Christmas party, that Bellatrix has been teaching Occlumency to her nephew Draco. As such, it is safe to assume that Bellatrix is a Legilimens herself, and so is confident in her ability to detect any falsehood from Snape. Snape's answers are carefully crafted so as not to trigger the ability of a Legilimens to know when he or she is being lied to; he probably also finds Bellatrix' abilities easy to subvert because of his practice with Voldemort.
Readers see Draco cast in a more sympathetic role here when it appears that he is Lord Voldemort's victim as much as his ally, forced to do his bidding under duress and at extreme risk to himself and his family. We will shortly see how a smug Draco initially revels in his own bloated self-importance at being appointed the Dark Lord's task, woefully unaware and unable yet to comprehend the probable consequences to himself and his parents should he fail. Narcissa, however, has correctly surmised Voldemort's true intention: to punish Lucius Malfoy through Draco. She is risking her own life by defying Voldemort in an attempt to save her family. This raises the question as to why so many Death Eaters faithfully serve Voldemort, who demands his servants' total obedience and loyalty while offering little reward in return, and who readily eliminates a follower or their family for any reason; even his most devoted and trusted confidants are capriciously expendable, even for the smallest misstep. This flagrant abuse could eventually create enough dissent and discord from within to undermine or destroy Voldemort's power, although, for now, his continued rise seems unabated.
Snape tells Bellatrix that his information led to the death of Emmeline Vance, who as we have seen is a member of the Order of the Phoenix. We will much later find out that Snape actually is working for the Order himself, as a double agent; it is safe to assume that Snape discusses with Dumbledore the information he will give to Voldemort. At the same time, we hear that Snape has only let those people die that he could not save. That strongly suggests that Dumbledore and Snape were somehow forced to give Voldemort information on Vance, and that they could not prevent her death. From this, we can assume that Vance's death was not preventable, Voldemort had already set his sights on her, but Snape had provided some small piece of information that had helped him find her. It is more than likely that Snape and Dumbledore had also provided Vance with the information that would allow her to fight back. While Vance clearly would not want to simply die, it is likely that she would agree to being put in harm's way, if in the battle she would have a chance to take some Death Eaters with her. While this is never confirmed, it is quite possible that, in fact, she did, and that the retreating Death Eaters had carried away and probably concealed their dead, as they tend to.
At the same time as we learn of Snape's true allegiance, we will learn that Snape's Unbreakable Vow, which would require him to kill Dumbledore in the event that Draco was unable to, was for Snape only reinforcement of a promise he had already made. The injury to Dumbledore's hand, which Harry will note in the next chapter, and which Snape here alludes to, is the outward sign of a curse that will take Dumbledore's life within a year. In a conversation that immediately follows Dumbledore receiving that injury, and so plainly occurs before the events in this chapter, Snape has reluctantly agreed to end Dumbledore's life himself, in order to save Draco's soul and spare Dumbledore's dignity.