Mortal Causes is the 6th book in the Rebus series. It tells of John Rebus investigating a shooting during the Edinburgh Festival with possible IRA connections, while also overseeing a new youth club that is attempting to unite protestants and catholics in a deprived estate.
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. And when the victim turns out to be the son of a notorious gangster Rebus realises he is sitting atop a volcano of mayhem about to erupt.