I was looking into the Agatha Christie Mystery Collection and apparently it contains around 100 books. There are the original 81 that came out in the 1980s and 90s, then there were a couple more sets added in the early 2000s. They also released a few title variants, where the book is the same, but it's the UK title instead of the US. The book I got at the thrift store for $2 is one of the rare variants and according to the website I found.. worth $$$$. Dang. That's awesome.