With no clear hero and lots of touristy establishing shots, Indian Summers may have started slowly, but it has built pace to become one of the most narratively satisfying dramas on British TV

Indian Summers had everything to lose before it even arrived. There were enormous advertising banners hanging everywhere, accompanying TV trailers, and journalistic speculation about it being Channel 4’s most expensive ever commission. Airing in the Sunday night slot, it was clearly intended to be a Downton rival, while its subject, the last days of the British Raj, was last covered in the seminal 1980s series The Jewel in the Crown. However were they going to land this £16m fish?

Carefully, it turned out. Indian Summers started slowly. Sooo slowly. It introduced us to a large cast, with no obvious hero. Set in the Himalayan hill town of Shimla, where the civil servants who run India relax on holiday, there was little to get the blood up. There was graffiti on a portrait of Queen Victoria, and the botched shooting of a senior private secretary, but really the first few hour-long episodes felt like a Technicolor travel brochure: an eye-popping camera crawl through verdant plantations and azure sky. It was lushly cinematographic, but leisurely, wilting in the heat of its own exoticness.

The main interest was a few Brits acting against type. Lovable Julie Walters plays Cynthia Coffin, a scheming, racist matriarch. Ostensibly running the town’s expat watering hole, she actually runs the whole town, manipulating and fixing events for the advancement of Ralph Whelan, secretary and possible successor to the Viceroy of India. An urbane, cunning man with a past, Ralph is played by Henry Lloyd-Hughes – familiar to most as Donovan, the school bully from The Inbetweeners. They’re a pretty rum pair.

Facebook Twitter Pinterest Julie Walters as Cynthia in Indian Summers. Photograph: Joss Barratt/Channel 4

There was skullduggery, but little forward momentum. Then, just past the halfway mark, the series picked up the ball and started to run with it. Its strength is storylines that tangle the personal and political. Cynthia and Ralph have falsified evidence linking Ralph’s near-assassin to India’s nationalist Congress party. This evidence is stolen by one of Ralph’s favoured clerks, Aafrin Dalal, perpetually torn between his Anglophile father, revolutionary sister Sunni and his love for Ralph’s sister Alice. There is a To Kill a Mockingbird-esque subplot, in which plantation heir Ian McLeod defends his business partner in court. The Indian is accused of murdering two people: a wild, homeless woman whose death could shake the British establishment, and Ian’s uncle.

This is only a snapshot of a claustrophobic, interconnected story in which every character has secrets, heroes quickly become villains – and possibly vice versa.

To say more would jeopardise a gripping mystery. It’s not perfect, and can be earnest – a touch more (or better) humour wouldn’t go amiss. But we shouldn’t judge on what it isn’t, but what it is: one of the most narratively satisfying dramas on British television at the moment, crammed with jackal-jostling for power, interracial hookups and the looming power of Gandhi, who we’ve not met yet, but who even offstage has a lightning aura.

Henry Lloyd-Hughes as Ralph in Indian Summers. Photograph: Matt Brandon/Channel 4

The UK is often accused of lacking televisual ambition compared with the US (even by George bloody Osborne, as if he’d know anything about it). Set in the 1930s and kept bubbling by the political fervour percolating through the country, Indian Summers is intended to run for 50 episodes, until independence is declared in 1947. The last throes of a great empire, a country that can smell freedom and the future – this is the stuff of which epics are made. It is a central component of British identity, our crucial passage from dominion to impotence, an episode we could do with knowing more about. With strong roles and equal screentime for women and non-white actors, it is also diverse, another area UK television can be notoriously bad in.

All of which wouldn’t necessarily justify your time if it wasn’t one of the most gorgeous, exciting shows around. If you are one of the 1.6 million viewers who dropped off before it found its stride, come back in, the water’s lovely. The first series finale airs on Sunday, and a second has been commissioned. If they can keep up the heat, these Indian Summers look set to last.