I think this is the first book of this author I’ve read.  He reminds me of Lee Child in that his main character (in this case a Private Investigator) kills people but you like him anyway.  The double in the title refers to a stolen painting Spero Lucas (the PI) has to track down.  There are a few other cases he’s working on (he hires out to lawyers) so the book has several plots to follow.  Also some very steamy sexual encounters!  I’m not sure if Lucas is a series character but I’m hoping so.