It is August in Edinburgh and the Festival is in full swing...A brutally tortured body is discovered in one of the city's ancient subterranean streets and marks on the corpse cause Rebus to suspect the involvement of sectarian activists. The prospect of a terrorist atrocity in a city heaving with tourists is almost unthinkable. When the victim turns out to be the son of a notorious gangster, Rebus realises he is sitting atop a volcano of mayhem - and it's just about to erupt.