The Dirty Duck (Richard Jury, #4)

"Nothing ever happens in Stratford," insisted Superintendent Richard Jury of Scotland Yard. Unfortunately, he was wrong. Besides the stage murders commited nightly at the Royal Shakespeare Theatre, a real one had been performed not far from the Dirty Duck, a popular pub. The victim had been a member of an exclusive group too: Those rare homicidal maniacs compelled to leave an intentional clue - in this case, a fragment of Elizabethan verse.
Now a nine-year old boy from the same tour had vanished and Jury was worried. For, if the killer intended to finish the rhyme, would it spell death for Stratford with each new line?