Takes place in book 5

Cassiopeia Black is the daughter of Regulus Black, but no one knows that of course. To the world she is known as Cassiopeia Walker, a Ravenclaw muggle-born. What happens when she starts to befriend the Weasleys, or more they try to befriend her?

When she somehow becomes close friends with Ginny Weasley the red headed girl starts to notice odd things about her. Like how every time anyting about death eaters is spoken she flinches.