• See more Daily Mail on Google - save us as a Preferred Source

Game of Thrones: The Mad King at Royal Shakespeare Theatre, Stratford-upon-Avon

Rating: Four out of five stars

'Welcome to Westeros' blinks the sign outside the Royal Shakespeare Theatre in Stratford-upon-Avon.

As anyone who hasn't been living under a rock for the past 20 years will know, this is a reference to the continent invented by George R. R. Martin as the setting for his string of bestselling fantasy novels that was turned into the blockbuster TV series Game of Thrones.

It became a global cultural phenomenon, regularly attracting more than 30 million viewers per episode.

The stage version prequel has been a decade in the making and, as soon as the production was announced, it was – predictably enough – an immediate sell-out.

On the face of it, it should be a surefire winner.

Playwright Duncan Macmillan has gathered together all of Westeros's major nobles for a jousting contest, the Tournament of Harrenhal, and the stage is set for a reassuringly familiar round of power plays, steamy love affairs, betrayals and rebellions.

Emilia Clarke and Kit Harington as Daenerys Targaryen and Jon Game in HBO's Game of Thrones

The concept has now been adapted for the stage in Game of Thrones: The Mad King. Pictured: Callum Woodhouse as Lord Robert Baratheon

Relative novices like me – who don't know a 'warg' from a 'skinchanger' (both magic beings) – will clutch at helpful straws, such as the striking white-blond hair of the mad king Aerys, host of the tournament, which marks him out as a member of the Targaryens, the family that rules Westeros for centuries.

I knew enough to grasp that dishy Jaime Lannister (Maxim Ays), just like the presumptuous Prince Hal in Shakespeare's Henry IV, shouldn't be climbing up the steps to Aerys's magnificent Iron Throne, a forbidding nest of jagged swords.

Especially when we know it's Robert Baratheon (a boorish, likeable Callum Woodhouse) who is going to grow up to be the king.

As mad monarchs go, Michael Shaeffer's Aerys is no Lear. Paranoid, petulant and dirty, he's more bad than mad. It is his casual cruelty and indifference to the suffering of others that makes him so scary.

The first half of Dominic Cooke's superbly staged, spectacular production has the feel of a dynamic Bayeux Tapestry: a stunning pageant of medieval stop-motion animation.

But after the interval, the plot takes off. Sparks fly romantically and dramatically, which is just as well because, at three hours 45 minutes, it's almost as long as Hamlet.

George R. R. Martin's fantasy novels were the inspiration for the blockbuster series

Michael Shaeffer's King Aerys II Targaryen is no Lear, writes Georgina Brown, and it is his casual cruelty which makes him so scary

But the pace never flags as huge mechanical horses powered by puppeteers thunder at one another, sending the jousting knights crashing to their deaths.

Stuffed with themes and echoes of Shakespeare's history plays and tragedies, it is when the epic becomes intimate that the Bard's influence is felt most keenly.

In the most moving scene, noblewomen – many of them pregnant – appear on balconies. Led by Catelyn Stark (Marty Breen), they sing a hymn: 'Gentle mother, font of mercy, save our sons from war, we pray.'

And suddenly this mythical fantasy becomes a play for today about the terrible waste of armed conflict, the sort of contemporary resonance calculated to attract a new generation to live theatre.

Game of Thrones runs until September 5.