Today’s Big Deal at Kindle UK is seven Hercule Poirot books by Agatha Christie for £0.99 each. Be aware, one of these, The Murder on the Links, is public domain in the US at least – and if it’s public domain here, it’s probably public domain in lots of other countries too, given how draconian US copyright is. If you live in the US or one of those other countries, you can find it for free at Project Gutenberg and other PD sites.
link to the Big Deal webpage at Kindle UK: https://www.amazon.co.uk/s/?node=4725112031