`Never write a biography," a colleague once warned me, "unless you are prepared to end up detesting your subject." The same might well be said of radio programmes. Surrounded by precarious piles of books on the history of Italian opera and the history of the Ottoman sultans, an ungovernable heap of CDs featuring Donizetti operas and Turkish military band music, scraps of paper covered with mad scribblings in several languages, cassette tapes which all featured irreplaceable interview material, yet which all looked dangerously alike, and a map of Istanbul which stubbornly refused to fold back into anything resembling its original pristine shape, I fell into a brief but black despair. Could a radio documentary called The Donizetti Mysteries ever emerge from this dog-eared mass of information? Well, it did, and it will be broadcast on FM3 on Saturday November 29th, exactly 200 years after the birth of the composer Gaetano Donizetti.

You either like Donizetti's music or you don't, and I loved it from the moment I was transfixed by the sound of a tenor voice - I think it belonged to Pavarotti - floating out the opening phrase of the famous aria Una Furtiva Lagrima, from l'Elisir d'Amore. But it was when, during the preparation for a lecture to Irish Times readers at the 1996 Wexford Festival on the subject of Donizetti's rarely-performed opera Parisina, I came across Herbert Ashbrook's brilliant biography of the composer, and listened to a crackly tape-recording of a luminous Montserrat Caballe in the title role, that I really got hooked on the Donizetti story.

Ashbrook's book reads like a thriller: the ascent from desperate poverty in early 19th-century Bergamo to the dizzying heights of European polite society; the effortless speed with which melody after melody, opera after opera, tumbled on to the stage; the dreadful denouement in which the dying Donizetti, crippled by an obscure form of cerebro-spinal syphilis, was held in virtual captivity in a French asylum for almost two years.

I wanted to know why. I also wanted to know why his music was often dismissed - after a brief nod at a handful of the more popular operas - in a manner which struck me as oddly personalised, as if the shadow of his illness had somehow fallen across the manuscript pages.

I also wanted to find out what happened to Donizetti's brother. Shades of Shakespeare's sister? Definitely. But for someone who had developed - ah, yes, but that's another story - a burning interest in Turkish classical music, the discovery that Gaetano Donizetti's elder brother Giuseppe had been appointed head of music to the armies of the Turkish sultan Mahmud II in 1828, had spent the rest of his working life in Istanbul and had apparently disappeared without trace, was absolutely irresistible. Research? Piece of cake. First, a trip into the depths of the Normandy countryside to pick the incredibly well-informed brain of Professor Alexander Weatherson, president of the Donizetti Society, who plied me with spontaneous hospitality, delicious wine and a wealth of food for thought about Gaetano Donizetti and his fatal, fateful illness.

Next to Istanbul, where - armed with documents and introductions from the unfailingly polite, helpful and efficient staff of the Turkish embassy in Dublin - I met the musicologist Resit Mehmet Erol, whose patient inquiries had uncovered one of the bestkept secrets of the Ottoman Empire - Giuseppe Donizetti's immaculate white marble tomb in the crypt beneath the Saint-Esprit Cathedral on Cumhurriyet Caddesi.

We drank tea in the smart cafe of the Marmara Hotel, wandered around the glorious maze of streets in Beyoglu where Donizetti Pasha once lived and spent a glittering couple of hours in the company of the pianist and composer Aydin Karlibel, whose insights into Turkish music were overshadowed only by his inspired performances of music by Giuseppe Donizetti and Franz Liszt. Eventually, of course, a script had to be written - at which point a great deal of hair was torn out, not just by me but also, I imagine, by my producer Celia Donoghue - who, despite all my missed deadlines and shattered promises, presented herself to me at all times as a veritable fount of enthusiasm, advice and calm.

There was a strange little footnote. On my return from Istanbul I phoned Prof Weatherson to ask if he had known of the existence of the tomb in Istanbul. No, he said, and nor - as far as he knew - did anyone else. But he had, while delivering a paper at an international symposium at the Donizetti birthplace, Bergamo, in September, made an interesting discovery of his own; the death mask so often reproduced in biographies of Gaetano Donizetti is not, it now appears, the death mask of the composer at all but that of his brother Giuseppe. Was it the revenge, or the kindness, of history which muddled in death the two brothers who had been so thoroughly separated in life - or was it just another Donizetti mystery, to be solved another day? Good. If I could even ask the question, I hadn't ended up detesting my subject after all.

The Donizetti Mysteries, written and narrated by Arminta Wallace, will be broadcast on RTE FM3 on Saturday, November 29th at 10 p.m.