Hardcover, used books. The name is written on the front of 3 books, they've been read through multiple times, moreso than the other books (1-9) from my other posts, but they still have plenty of life left. Book 10 looks the worst on the spine, but all are fully intact. Books 10-13 of the series: The Slippery Slope, The Grim Grotto, The Penultimate Peril, The End