Nine for the Devil by Mary Reed & Eric Mayer (historical fiction - mystery)

Apparently I'm missing out on something, because this is the ninth mystery in the series written by a husband and wife.  This particular book uses the emperor Justinian's growing paranoia to shed light on the political situation in Constantinople in 548.  I'm not a big fan of mysteries, but I liked this book's fast pace and plot twists, so I won't give any spoilers.