Book 6 | Ch:02 - Spinner’s End

SPOILERS:

Narcissa goes to visit Snape in secret against Voldemort’s orders, and Bellatrix tries to stop her but ends up joining her at Severus Snape’s house anyway. Snape prevents Wormtail’s from eavesdropping their conversation and then tells Bellatrix his story. She still refuses to trust him. Narcissa then reveals that Voldemort has ordered her son Draco to do something extremely difficult, and asks Snape to make an Unbreakable Vow. He accepts, saying that he will help Draco carry out the deed, and even perform it himself if Draco were to fail.