The Golden Tresses of the Dead is the tenth and most recent (2019) in the (excellent IMO) Flavia de Luce series by Alan Bradley. It has dropped to £3.99 at Kindle UK. This is a really enjoyable series set in a 1950s English village, and featuring 11-year old Flavia, who is a precocious junior chemist and part-time sleuth, as the protagonist. Also, it’s not really on sale in the US but it has been priced at $4.99 for quite a while, which is not too too bad for a most-recent-in-series title.
The Weed That Strings the Hangman’s Bag is the second in this series. It has dropped to £0.99 at Kindle UK: https://www.amazon.co.uk/dp/B003FXCSMM
The Golden Tresses of the Dead has now dropped to £2.99 at Kindle UK. The link in the OP is still good…
The Grave’s a Fine and Private Place is the ninth in the series. It’s on sale right now at Kindle and Kobo US for $1.99.
Kindle US: https://www.amazon.com/Graves-Fine-Private-Place-Flavia-ebook/dp/B071VHV946/
Kobo US: https://www.kobo.com/us/en/ebook/the-grave-s-a-fine-and-private-place-2
Speaking from Among the Bones is the fifth in Alan Bradley’s excellent IMO Flavia de Luce series. It has dropped to $1.99 at Kindle and Kobo US.
Kindle US: https://www.amazon.com/dp/B008ZPG8XK
Kobo US: https://www.kobo.com/us/en/ebook/speaking-from-among-the-bones-1
A Red Herring Without Mustard is the third in the series. It’s £2.99 at Kindle UK right now: https://www.amazon.co.uk/dp/B004R9Q1NA
Also, The Golden Tresses of the Dead is still £2.99 at Kindle UK, and the link in the OP is still good.
The Sweetness at the Bottom of the Pie is the one that started it off – the first in the series. It’s $1.99 right now in the US…
Kindle US: https://www.amazon.com/dp/B0027G6XDS
Kobo US: https://www.kobo.com/us/en/ebook/the-sweetness-at-the-bottom-of-the-pie-2