Harry Potter and the Half-Blood Prince, released on July 16, 2005, is the sixth of seven planned novels in J.K. Rowling's popular Harry Potter series. Set during Harry Potter's sixth year at Hogwarts, the novel explores Lord Voldemort's past, and Harry's preparations for the final battle amidst emerging romantic relationships. In 24 hours, the book sold 6.9 million copies in the United States alone, or 287,564 books per hour, making it the fastest selling book in recent history. It generated over £100 million in sales on its opening weekend, outpacing even the combined take of the top movies at the box office that same weekend. Bookseller Barnes and Noble reported sales averaging 105 copies per second in the first hour of sales. The book is dedicated to Rowling's daughter Mackenzie, who was born in the middle of writing this book.