Today's Big Deal on Amazon.co.uk is 19 of Ellis Peters "Brother Cadfael" books, all at 99p
https://www.amazon.co.uk/b/ref=s9_ac...d_i=5400977031
There may in fact be 20 or 21
A Rare Benedictine: The Advent Of Brother Cadfael (The Cadfael Chronicles) is unnumbered.