On 20 May 1609, the publisher Thomas Thorpe stepped off Ludgate Hill into Stationers' Hall, and registered what was to become perhaps the most famous poetic works of all time: Shakespeare's Sonnets. It was a slim volume on publication, containing 154 poems over 67 pages, and the edition is now extremely rare: only 13 copies survive. But its influence has been all-encompassing, providing a template for language, for literature, for love, ever since. Recent years have seen the sonnets disseminated in ways that Shakespeare could never have imagined. "Shall I compare thee to a summer's day?" is quoted 5m times on the internet. Apps have been created in which famous voices recite the poems, sonnets are tweeted, T-shirts are printed, and poetry that was once said to circulate only among Shakespeare's "private friends" is now stored for ever in the cloud.

Yet despite the popularity of the sonnets, their mysteries continue to puzzle readers. Who were the young man and "dark lady" of the poems' sexual intrigues? And did Shakespeare want these poems published, or kept private? Literary theory advises against such biographical speculation. Yet modern bibliography stresses the messier side of literary life: that texts are physical not abstract entities; that printers were sometimes pirates, not always with their author's interests at heart. In addition, text databases such as Early English Books Online allow one to isolate the unusual aspects of a writer's vocabulary, and therefore suggest what they might or might not have written. And these techniques help to link together a series of exciting discoveries about the sonnets: that an arch-rival of Shakespeare's may have masterminded their publication; that their publication was therefore an act of revenge; and that the "dark lady" at the centre of the story was not a poetic fiction but a real person....