The Leftovers isn’t easy watching. The premise is a tough one: roughly two percent of the world’s population suddenly vanishes one October day, leaving the other ninety-eight percent to agonize over where they went, why they went, and what the hell actually happened. Three years on, the weight of the uncertainty left in the wake of the event is so fresh that it might have happened just yesterday. Justin Theroux stars as Kevin Garvey, Chief of Police in smalltown Mapleton, New York, and in the pilot episode it’s already clear what kind of devastating effect the disappearance has had on Mapleton and on Kevin.

Damon Lindelof is a major player here, the writer behind such other head-scratchers as Lost and Prometheus, and his stroke is evident in the first hour of Leftovers. This is one reason why the show likely defies those happening upon it as they lounge on the couch and flip through channels until they hit HBO – The Leftovers isn’t at all a casual watch. Lindelof shares creator credit with Tom Perrotta, who wrote and published Leftovers as a novel before turning it to the small screen, and it appears they’ve both adopted the “mystery box” theory posed once by J.J. Abrams. The Leftovers shows us the box, shows the top and bottom and sides and practically makes us beg to see what’s inside it – and Lindelof and Co. are aware that that mystery itself is more compelling than actually opening the box. The main box – containing the answer to the question where did the departed go, and why were they taken? – is the framework for the entire show.

One difference from previous efforts Lost and Prometheus might be that The Leftovers doesn’t really seem like it will actually ever open that box; this is apparent even after the first episode. Mining the emotional fallout from such a freaky and indiscriminate occurrence seems to be the focus here, and it’s a refreshing focus at that. Lost and Prometheus opened the mystery box in different ways – Lost succeeded in grand fashion where Prometheus did not – but the best parts of both were in those head-scratching WTF moments of pure mystery. That’s promising for The Leftovers, both in the short- and long-term game.

The pilot takes place on the three-year anniversary of the event (which some have dubbed The Departure), since declared a national holiday of remembrance. Mapleton, like every other town, is having a Heroes Day Parade. This is where most of the disparate threads we’re handed at the beginning of the episode begin to come together: Kevin is tasked with the public peace at this powderkeg gathering, Kevin’s daughter Jill attends either to truly reflect on those who’ve left or just to piss her dad off, a minister played by Christopher Eccleston asserts his position that The Departure was not The Rapture, and the cult known as the Guilty Remnant shows up to stir all of these ingredients until the pot boils over.

As with Lost, there’s a healthy amount of symbolism here that demands outright attention. This is one reason why The Leftovers is tough to watch, because the deer and the dogs that Kevin encounters are clearly meant to represent something and because that something is not, in fact, very clear at all. But while the symbolism and ambiguity and WTFness of The Leftovers could conceivably be formed into a bite-sized weekly morsel, it’s the emotion and pain that those who’ve been left behind still feel that really makes The Leftovers a demanding series. On one side of the coin the show is a puzzle, a game that we can piece together week by week; the flip side appeals not to the brain but to the heart, cheesy as it might sound, and it’s a major virtue of the series that you’re unable to take one side without the other.

So The Leftovers isn’t easygoing viewing, but it is one of the most important new shows of the past year.