His superiors plan to bury him alive in the paperwork of a long-running war crimes investigation. But a more immediate problem gives Rebus an excuse to wriggle from under the pile. Rival gangs are fighting for control of Edinburgh's criminal economy. A shady Japanese business consortium cosies up to one gang leader for sinister reasons of its own. A gang victim comes to Rebus for help - a Bosnian refugee pushed into prostitution, who has an extraordinary resemblance to Rebus's daughter. The case takes on a viciously personal twist when the daughter is the victim of an efficient hit-and-run attack.
But the other investigation still demands attention. It deals with a different war and a different type of refugee - a junior SS officer implicated in a massacre of French civilians (closely based on the all-too-real Oradour massacre of June 1944). Is this the same man who, half a century later, lives in wealthy retirement in Edinburgh's Heriot Row and dabbles happily in Babylonian history and astrology? If so, this opens up a wider issue, for Rebus and for us: the hundreds of Nazi war criminals who, with the connivance of Allied governments, escaped via the "Ratline" to comfortable new identities.
Rankin has followed one success with another. Sardonic and assured, the novel has a powerful and well-paced narrative. Echoes bounce between the two sides of the story. The Hanging Garden - the title comes from a song by The Cure - contains a wealth of characters who have been, will be, or richly deserve to be hanged. Fortunately, if predictably, Rebus himself is one of the exceptions: the hard-boiled carapace does not entirely mask the soft centre.
There is nothing new in the maverick but heroic detective. What is striking is the way Rankin uses his laconic prose as a literary paint-stripper, scouring away pretensions to reveal the unwholesome reality beneath. This crime novel holds a mirror to modern Scotland, and in particular to its capital city. The reflection is not, on the whole, a pretty sight. Rankin's Edinburgh is not a town for faint-hearted coppers.
Above all, though, what lingers in the mind is the sense of moral outrage that informs the book. At one point a Jewish historian working for the Holocaust Investigation Bureau asks Rebus a question: "Can time wash away responsibility?" Rankin leaves Rebus and the reader to find their own answers.