The C.I.D Room is (not that surprisingly) the first in the C.I.D. Room series by Roderic Jeffries. It’s free right now (April 1, 2021) at Kindle US and UK. The titles in this series go free rarely, but often enough that if you have some patience (a couple of year’s worth), you can probably pick them all up for free. Keep an eye on this blog – I”ll post them when I see them.