EARLY ON IN HIS WRITING career, Ian Rankin took the decision that his Edinburgh detective, John Rebus, would grow old in real time.

He did not wish to follow the example of Ruth Rendell, who once revealed that her policeman hero, now Chief Inspector Wexford, was 52 when she created him in 1964; he’s still in his job, 43 years later. The same span covers the career (so far) of P. D. James’s Adam Dalgliesh – first encountered in 1962, and most recently in 2005 – although he is a little younger than Wexford, and has at least been frequently promoted, rising to the rank of Commander at Scotland Yard.

John Rebus – then a detective sergeant nearing 40 – was introduced in Knots and Crosses, published in 1987. He’s now about to turn 60, the age at which members of the police in Scotland have to retire. Rankin has no option. Rebus must go – despite a plea by one Scottish parliamentarian for the retirement age to be raised to 65, so allowing Rankin to fit in a few more novels. Exit Music– a title revealed only a couple of weeks ago after intense secrecy – is the 17th and final Rebus novel.

Except that it might not be. I interviewed Rankin at the Hay-on-Wye literary festival in May, and he admitted that he would find it difficult to make a clean break with his creation. Perhaps, he mused, Rebus could return in some capacity, although nothing as obvious as being recalled to the Edinburgh force to help them to solve a sticky mystery. Why was he finding it so hard to let go? Because, he replied, he hadn’t quite got to the bottom of Rebus; there were still things he wanted to find out about him; there were unresolved issues.

In the context of Rankin’s desire to have his detective to age in real time, that remark points to an important element in the success of the Rebus saga. Every book revealed something new and interesting about its hero.

Readers weren’t merely told excellently plotted tales about solving crimes in Edinburgh; the books encompassed an intriguing journey through the emotions and psychological make-up of a difficult, sometimes tormented, but ultimately sympathetic man who happened to be a policeman.

As Rankin got better and better as a writer, so Rebus became an increasingly complex and fascinating character. We still want to know more about him, just as he is being taken away from us. That is the author’s dilemma as well as that of his readers.

There is a second reason why it was so necessary for Rankin to set his novels in real time. It has enabled him to use political and social developments, and contemporary events, not just as a back-drop but as integral elements of Rebus’s inquiries. The crucial action in The Naming of the Dead last year, for example, took place during the 2005 G8 summit.

Other works have marked burning issues: drugs, paedophilia, racism, the plight of asylum seekers, trafficking in prostitutes from Eastern Europe, the construction of the outrageously expensive Scottish Parliament building. The title Exit Music serves a dual meaning – not just Rebus’s exit from the police but also the possibility of Scotland’s wishing to leave the Union with England after the recent election results.

Exit Music cannot be read on the same terms as any other Rebus novel. Such has been the publicity surrounding its status as the detective’s swansong, that it is impossible to judge it purely on its merits as a crime story, or as just another book in a series. I would not recommend anyone who has yet to read a Rankin to start with this one. Some of its impact will only be fully appreciated by those who have a certain familiarity with Rebus and his entourage.

The action covers the ten days before his final departure. Rebus investigates the killing of a dissident Russian poet, found in a car park and apparently the victim of a mugging. Is the killing personal, or somehow tied up with the presence in Edinburgh of a bunch of Russian businessmen?

There’s another murder, and Rebus (unexpectedly complying with the smoking ban) is being leant on by local moneymen, politicians and his own superiors. He reacts with customary insubordination, and gets into big trouble, even as his last day approaches.

Also active, and connected with the Russians, is his long-time adversary, the gangster chief Big Ger Cafferty. There is a mysterious woman in a hood, a new copper whose grandfather was arrested by Rebus many years before, and even a subplot with Rebus himself under suspicion.

On the personal front, readers will be anxious to know whether their wish for the furtherance of Rebus’s relationship with Siobhan Clarke, his sidekick over the past 13 books, is to be granted.

There is, thankfully, no glib conclusion to tie up all the loose ends or suddenly to clarify and explain Rebus. On the contrary, he leaves the stage the irresistible, infuriating enigma that he has always been.

Exit Music is a fitting end to the career of one of the most beguiling characters in the history of crime fiction – not because the lowering of the final curtain finds the audience satisfied, but because it leaves them gasping for more. I hope that Rankin does not succumb to the entreaties to resuscitate Rebus, à la Sherlock Holmes, by finding work for him in his retirement or, even worse, by remembering past experiences that unaccountably failed to find a place in the novels already published. Let the Rebus books stay as they are.

Exit Music by Ian Rankin

Orion, £18.99; 380pp

Buy the book here at the offer price of £17.09 (free p&p)

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