One balmy evening two summers ago, I stepped into a London pub in the hope of a quiet drink. It was 9pm on a Monday, but the Three Compasses was already jammed. A chorus was being led by a group waving their beers like conductors’ batons. Couples were clinging to one another. At one point a young man stood up, pointed at a projector screen and yelled: “Get a grip, Theon!” Monday nights, it transpired, were Game of Thrones nights.

If similar scenes have played out in homes and bars around the world in recent years, this weekend they will be even bigger. The final season of HBO’s fantasy epic arrives on a tide of cultural anticipation unseen since the climax of Harry Potter. So far, the trailer has been viewed more than 50m times on YouTube. Over seven juggernaut seasons, the most ambitious TV show of our era has become a phenomenon that is casually referenced by politicians and novelists as a byword for the most brutal and cynical way of wielding power.

At the centre of the Game of Thrones universe are two questions: one, how a strange work of fiction — which features, among other exotica, dragons, eunuch warriors and the living dead — came to have such a hold on our culture; and two, how it’s all going to end. For as the show careers towards its finale on May 19, we are heading for one of those once-in-a-decade events in which it is almost unseemly not to take an interest.