( Sorry for the lack of links, but my internet is flaky right now)
Murder at the Vicarage by Agatha Christie is free at BN.
Fatal Destiny by Marie Force is free at Amazon, BN, Sony, Kobo and Carina Press.
Bright Young Things by Anna Godbersen is a free pre-order at Amazon ( US only).
Once a princess by Sherwood Smith is available for free at Amazon and BN.
Alexandra’s Legacy by N.J Walters is available for free at Amazon and BN.
The Witch of Agnesi by Robert Spiller is available for free at Amazon and BN.