The Name Of The Rose by Umberto Eco.
Join me if you will for a journey to the wild and lawless world of 1327, where bands of rogue monks roamed the land, a-theoligisin' and a-quibblin' over minor points of biblibal interpretation, and occasionally a-disagreein' to such an extent that they had no way of a-resolvin' the argument other than for one side to set the other on fire a bit until they shut up.
Into this hive of scum and villainy one monk, William Baskerville, walks alone - a maverick monk, who doesn't play by the book, but God dammit he gets results. Dammit, chief, if I haven't cracked the case by vespers the senior abbot can have my badge! Dammit, Baskerville, you're too close to this one - you're off the case! Go and investigate those potato thefts from the lower kitchen.
I'm not sure I can keep this up for a whole review, to be honest, so let's start again. It's 1327, during the period (1309-1377) when the Catholic popes resided in Avignon rather than Rome. As part of the ongoing theological wranglings over this situation, the aforementioned maverick monk William Baskerville and his young sidekick Adso travel to a monastery in northern Italy to attend some formal discussion about Biblical interpretation, which would of course seem laughably trivial were it not for the distinct possibility of occupying the wrong side of the argument getting you taken outside and set on fire. William is particularly at risk in this area as he is a big fan of the newfangled empiricism and critical thinking as expounded by Roger Bacon and William of Ockham, ideas some would feel were dangerously inimical to religion (and they would of course have been right).
Anyway, other matters soon arise to occupy the monks - one of them is found dead, having apparently thrown himself out of a window in the monastery's library, access to which is jealously guarded, lest dangerously subversive texts should be seen by those not well-enough versed in sophisticated theological ignoring of reality to be immune to them. Hot on the heels of that, and amid lurid rumours of some hot forbidden monk-on-monk action, another monk is found upended in a vat of pig's blood, another is found drowned in the bath-house, another has his head caved in with a religious ornament and another keels over in the prayer-stalls, apparently poisoned.
William's awesome powers of deduction eventually enable him to crack the secret code that leads to some hidden rooms within the labyrinthine library, the solution to the mystery and the person behind the killings. After a classic let-me-explain-my-evil-plan manoeuvre followed by a textbook you'll-never-take-me-alive gambit the whole library, and subsequently the whole monastery, ends up going up in flames, with the book that was the key MacGuffin consumed as well.
A 500-page book, large sections of which are devoted to descriptions of the machinations of corrupt 14th-century religious types and arcane disagreements over scriptural interpretation, even while interspersed with monks being offed in entertainingly lurid ways, won't be for everyone, especially as the aforementioned MacGuffin - the legendary lost second volume of Aristotle's Poetics, supposedly a scholarly study of comedy, which the (admittedly insane) antagonist thinks is going to destroy religion by making people laugh at it, is a bit on the disappointing side after all the build-up. And William's theory that this is all some sort of hugely complex serial-killing spree based on the book of Revelation turns out to be a great deal more coherent and interesting than the actual explanation. No doubt that's all part of Eco's fabulously post-modern plan, though. The book is supposedly chock-full of literary allusions and puns, the odd one or two of which I spotted, most obviously that William of Baskerville is basically Sherlock Holmes in a habit.
It's all much more fun than a novel about 14th-century monks has any right to be, though. I haven't seen the 1986 film, though that didn't stop me visualising William as Sean Connery throughout. I can only assume that the film omitted much of the theological discussion, or it would have been about eight hours long.
The Name Of The Rose won, in addition to most of the significant Italian literary awards, the Prix Médicis étranger in 1982, which means it qualifies as an addition to the list here.