The Sweetness at the Bottom of the Pie is the multi-award nominated/winning first title in the Flavia de Luce series by Alan Bradley. It has dropped to $1.99 at Kindle and Kobo US, possibly for today only since it is part of the US Kindle Daily Deal.
Kindle US:
https://www.amazon.com/Sweetness-Bot...dp/B0027G6XDS/
Kobo US:
https://www.kobo.com/us/en/ebook/the...m-of-the-pie-2