The great handicap of HBO’s new four-part costume drama Catherine the Great (Sky Atlantic) is that she’s not Henry VIII. Little common knowledge can be assumed and an awful lot of time and effort has to be spent explaining quite where we are and who has done what to whom to get us there. An opening caption sets the scene, which you can choose to read in your A-Team or Star Wars voice: “Catherine’s turbulent reign began in 1762 with a military coup. She seized power from her husband Emperor Peter III who died soon after – in mysterious circumstances. Surrounded by enemies and fighting off rival challenges to her throne, Catherine’s rule is far from secure.” If you have a problem, if no one else can help you, maybe you can hire … Count Orlov and Grigor Potemkin. No, wait, I’m getting ahead of myself.

Catherine the Great is played, magnificently, by Helen Mirren. If she were not, questions would surely be asked in the House. Her formidable talent and long career has made her into acting royalty herself and in recent years she has become a specialist in monarchs proper, leaning into her innate regality to produce award-winning turns as Elizabeths I and II. Even more pertinently for her latest venture, she was also born Helen Mironoff, daughter of Vasily Petrovich and granddaughter of Pyotr Vasilievich Mironov, a colonel in the Imperial Russian army. It feels as much a labour of love as the glad seizing of a part that would be catnip to any actor.

So this series has the perfect actor and comes, in many ways, at the perfect time – ripe for the story of a woman resented on all sides for refusing to shape herself or her desires to the traditional feminine mould and becoming instead the embodiment of the writer Florence King’s note: “When a woman steps out of her place, she always steps up.” Not all of them arrange a coup d’etat removing their husbands from power and having them assassinated (she maintained plausible deniability over the latter), of course.

Her now-lover Orlov and his brother are angling for a slice of power. The army reckons it put the Empress on the throne and can knock her off it any time. There are those who consider her regent only until her son Paul reaches his majority and can take over. There are others who have met Paul and would rather a large fur hat governed Russia than that 18-year-old milksop. And then there’s Prisoner Number One, poor Ivan VI, a claimant to the throne confined in Shlisselburg prison for all of his 24 years and sent mad in the process, but who still acts as a rallying point for Catherine’s opponents.

Before long we are all in a welter of intrigue, treachery and general skulduggery – and once Potemkin heaves into view, you can add sexual rivalry too. It really is, one hopes, so unlike the home life of our own dear queen.

In the opening episode, the liberal-minded empress must lose some of her ideals and find her cojones instead. Ivanites move against the empress, so her orders to have him killed are carried out. The army’s Lieutenant Merovitch tries to stir up trouble and finds himself decapitated, despite her insinuation of a pardon on the scaffold. Only Potemkin offers her a safe space, and he is soon defenestrated by the Orlovs for his pains. He survives, though only to have to attend a fancy dress palace ball (which hardly seems fair on the man).

The parts are all good – the scenery, the performances, the script – but they add up to slightly less than their sum. Perhaps it is the extra exposition that makes it feel too ponderous and prevents it from taking flight. Or perhaps it is the fact that when it comes to creating anything, you can do all you can to maximise your chances of success but the final ingredient is always elusive. Call it magic, call it luck, but you need it to alchemise your efforts. If it’s not there what you have is a sturdy workhorse, full of fine actors, good moments and impeccable intentions, but not the elegant thoroughbred or racing steed of your dreams.

• This article was amended on 4 October 2019 because an earlier version referred to Prisoner Number One as Ivan IV when Ivan VI was meant.