Preview: Striggio, Royal Albert Hall, London

One of the key works of the Renaissance was consigned to obscurity because an 18th-century priest misspelt the composer's name while doing an inventory of the biggest manuscript collection in France. The rediscovery of Alessandro Striggio's mass Ecco si beata giorno – and its Proms performance – marks the conclusion of an extraordinarily tangled tale, and casts new light on a quite separate musical mystery.

That mystery concerns Thomas Tallis's 40-part Spem in alium, which choirs regard as their Everest. It was long believed that the idea for this work sprang fully-formed from the composer's brain. That was until the discovery of a London law-student's anecdote in 1611, which told of an Italian work that made such "heavenly harmony" that a music-loving duke asked "whether none of our Englishmen could sett as good a songe", whereupon Tallis took up the challenge. Striggio's 40-part motet Ecce beatam lucem was identified as the spur. Mystery solved?

Not quite. Twenty years ago, the harpsichordist-musicologist Davitt Moroney, who conducts the mass's performance, was rooting about in the Bibliothèque Nationale in Paris when he stumbled on a reference to a 40-part mass by a composer whose name he did not know. Instinct told him this must be something other than Striggio's motet. Since the collection the work was taken from comprised 10,000 items, and since the name drew a blank, he shelved his search, because he was looking for a needle in a haystack.

A few years later, a French musicologist casually told him about a "rather mad" 17th century 40-voice mass in the library's vaults, but since the century was the wrong one, he didn't connect it with 16th-century Striggio. Then, two years ago, a scholar who'd spent decades patiently cataloguing the collection gave him a new clue, and with one click he was home. "I immediately realised I was looking at one of the greatest lost works of the Renaissance," he says. "It was like winning the lottery."

Prom 6, 17 July. Visit Independent.co.uk/promcast for exclusive daily podcasts. Join Nicola Christie as she talks to composers, musicians and Prom-goers. Plus, listen online to the Proms 2007.

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