In the short story Swan Song, Edouard Bréon was an retired French baritone. He is the neighbour of Lord and Lady Rustonbury. When Signor Roscari fell ill, M. Bréon was asked to take over the role of Scarpia and sing with Paula Nazorkoff in her role as Tosca.
At the end of the performance, when Tosca stabs Scarpia in the opera, Madame Nazorkoff really stabs Bréon and he dies. Why she does so relates to events in their past (see the plot summary for details).