Alter Ego by Elizabeth Linington
 
Mystery writer Brendan Monroe is tormented by the fear that his flamboyant fictional detective P. I. Roy Barron has come to life. Is the author losing his mind? Or is someone making it seem that way? When Barron is found dead, Sergeant Dan Valentine of the Santa Monica police focuses his investigation on the local chapter of the Mystery Writers of America, where he faces the fascinating challenge of trying to trap a murderer whose profession is devising diabolical plots.
 
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