Death among rubies

Lady Frances Ffolkes is incensed when she finds out that her dear friends Gwendolyn and Thomasina have been subject to vicious threats. Promising to uncover their attacker, she travels with them to Kestrel's Eyrie, the fabled estate belonging to Gwen's family. But soon Frances faces an even greater problem, when Gwen's father, a powerful diplomat, is stabbed to death with his prized ruby dagger.