We can only presume that the half-naked man's nipples are solid as hardback bibles as he stands shivering on the church steps. That's because his torso, though bare, is covered by a placard that decries him: "fornicator".
Welcome to a tour of medieval London, Dr Matthew Green style. The rakish prof has whisked us back to 1390 and the walled bastion of 40,000 tortured souls with help from a group of actors willing to brave the January afternoon in thin cassocks and, in the case of this particular fornicator, less.
But although middle ages London was a place where public shaming was dished out more often than decent drinking water, there was sweet succour to be found by those who could afford it — not foaming pots of ale, but gold-laced coconut shells brimming with wine. Medieval London, you see, was a city of oenophiles — and this is the refreshing angle our be-gobleted guide takes with his brand new walk.
Our journey begins in sobriety, at the palimpsest of Guildhall, from which we make our way down Cheapside — a thoroughfare that once clattered with the sound of jousting knights. Green brings the old city to life with frequent interludes from his troupe — there's an early fracas between an alderman and a monk which startles a couple of passers-by — but it's his vivacious delivery and trickling of trivia (did you know curfew means 'to cover fire?') that really quenches your thirst for knowledge.
As for quenching actual thirst; a pit-stop is taken in the depths of a City drinking den, where we learn that London didn't just import wine from France, Italy and Spain — the city was patchworked with its own vineyards, and the weather was far milder, even than what we've been used to lately.
We resume at the former vineyards of London, where we run into more characters from the past: the wife of a wine merchant killed by the Black Death and the fittingly splenetic patron saint of London, Erkenwald, who abused his position by 'vinegaring' down the vino and is now only remembered by a street name in East Acton.
There's also an incident in which an anchorite, supposed to be confined to a small cell for the rest of his life, has been sent to the wrong church by Google Maps. Let's be honest — with so much wine flowing, you have to expect the odd hiccup.
By the time we're sipping our final goblet at Queenhithe our heads are brimming with trivia on a drinking culture that had previously eluded us. Time to jot some of it down before the malmsey washes all that knowledge away.
Dr Matthew Green's next medieval wine tour is on 20 February. Tickets £29.14-£36.01