Cassandra Black is the only daughter of Sirius Black. Raised by her father's cousin, Andromeda Tonks, Cassandra is now entering her third year of Hogwarts as a Slytherin student. But things are different this year. Dementors surround the school, all of Hogwarts is on high alert, and Harry Potter has suddenly taken notice of her — not the good kind. And it's all her father's fault.