Book review2-06

I read this book, this is Blackmail.
First, I thought Black mail, What is Black mail??
This book not appear about mail?? What is the mail?

Jo has boyfriends who is Dave. But sometimes she can't understand him.
Jo worked at rich house to clean them before. Her boyfriends asked her about rich house.
Few days later, her boy friends steal something at rich house,
he is really bad man.
And, he blackmailed her.
This is really scary story.