Things take a gruesome turn when Ferrabees Circus comes to town, bringing with it a chain of sinister clown sightings, threatening notes, and deathly dangerous circus acts.

When Mahesh Sidana - butterfly collector and founding member of an elite IQ society - is found murdered, pinned to a wall in a manner akin to his treasured butterfly specimens, DCI Barnaby and DS Winter are thrust into a crime that impacts not only on their community, but internationally. With the help of an old friend, can they catch the culprit before another victim is found?