The super wealthy are at it again: embroiled in jealous feuds, whispering behind each other's backs, completely miserable, staring pensively at the churning ocean from the balconies of their clifftop mansions. Brutally murdering their enemies at school fundraisers. The usual sort of thing.

The basic premise of SoHo's latest HBO mini-series Big Little Lies sounds like it could be some kind of dreadful B-movie. In different hands it's easy to imagine an adaptation of Liane Moriarty's bestselling novel turning out that way.

Instead, writer David E Kelley (

Ally McBeal

) and director Jean-Marc Vallée (

Dallas Buyers Club

) have gone all-in, with the help of a sensational cast (Reese Witherspoon, Nicole Kidman, Shailene Woodley, Alexander Skarsgard ...), and turned it into one of the must-watch television shows of the year.

The show is ostensibly a murder mystery: someone was bashed to death at a fundraising event at Otter Bay Elementary, the decile one-million school where the main characters' kids all just started first grade. The first episode begins with the detectives and the blue and red flashing lights, then loops back to the first day of term to introduce the key players.

Jane (Woodley) has just moved to Monterey, California, with her son Ziggy. She makes an ally in Madeline (Witherspoon), the high-energy mother of Chloe, a 6-year-old girl seemingly possessed by the soul (and music taste) of a sarcastic 60-year-old man. Madeline is friends with Celeste (Kidman), mother of twin boys who whirl around her like a hurricane, armed with toy guns.

Are the guns foreshadowing some terrible act of violence? How about when Madeline gets out of the car to berate some text-driving teens and Chloe wisecracks from the back seat: "You're dead!" That one's definitely foreshadowing. But it's too obvious, surely. A red herring.

Reese Witherspoon produced Big Little Lies in an attempt to bring more female-centric stories to the small screen.
Reese Witherspoon produced Big Little Lies in an attempt to bring more female-centric stories to the small screen.

So we don't know who dies, or who kills them (unless you've read the book). But we do get some clue as to why. The first episode's big flashpoint seems innocuous at first: a classmate accuses Ziggy of choking her on the first day of school. He denies it, the girl's mother demands an apology. Sides are taken, passive aggressive words are exchanged at the school gate, ancient vendettas bubble to the surface.

"It all goes back to that incident on orientation day," remembers one of the witnesses, whose testimonies punctuate the first episode. Another, which sounds a lot like a Real Housewives soundbite: "Things never blow over once Madeline gets involved - they blow up."

The show is pitched as a "dark comedy-drama", but the comedy part can be hard to spot. Was 6-year-old Chloe thrashing obscure '70s crate-digger prog on her iPod meant to be funny? Maybe children of extreme wealth just read a lot of Mojo magazine. Between the dread-filled handheld camera and ominous flash-forwards (a sinister lurking child, an unidentified footprint on the beach ...) the first episode seemed more psychological thriller than anything.

More so than most mini-series, this felt like the first part of a six-hour movie rather than a standard episode of television. This meant more long, brooding, cinematic sequences - gazing intensely out over the ocean and all that - and a more slow-burn pace, but for the most part this was something to savour rather than fast-forward through.

Solving the murder case quickly became secondary to unravelling the characters' complex personal lives and interpersonal relationships. The mini-series format allows time to develop each one beyond an empty caricature - this is where the show's real strength lies, and why it promises to make for increasingly addictive viewing.

• Big Little Lies screen on Soho, Sunday, 8.30pm and is available on Neon.