William Stafford 
Assassin and His Sister [PDF ebook] 
A Comedy of Murders

Italy during the Renaissance and Sparafucile and his sister strive to make a living bumping off any unfortunate rich man who happens across their path. The trouble is: as an assassin, Sparafucile is not what you might call competent and his unpredictable sister seems to be spiralling out of control. Inspired by characters in Verdi’s Rigoletto, this is an action-packed, fun-filled visit to a world of intrigue and betrayal, from the author of Leporello on the Lam.