The opening half hour of The Riches (8.30 Mondays on Showcase) is probably the most exciting television I’ve seen all year. Not exciting in a James Bond sort of way, but exciting in the deftness of its storytelling, the richness of its characters, and the sheer audacity of the questions it asks.

The Malloys are a family of gypsies. Travellers. Thieves. They move from con to con in their enormous Winnebago, never staying long enough in any one place to be found out. But in a moment of carelessness, they’re involved in a car accident, killing the unfortunate married couple in the other car.

An investigation of the wreckage reveals that the late Mr and Mrs Rich are on their way to their new dream home in a new community where no-one knows them. It’s here that the Malloys are confronted with the show’s central questions. Can they move into the house and assume the identity of the Riches? Can they live like ‘buffers’, normal folk? Can this motley family of travelling thieves actually steal the American dream?

If that’s not a premise to get your heart racing, then TV isn’t for you. But, of course, a premise alone does not a great show make. It’s the way characters respond to that premise and the challenges it throws up that makes great drama. And The Riches is well on the way.

It’s TV on the margins; the latest in a tradition of American television (The Sopranos, The Wire, Deadwood) that gleefully blurs the distinction between good and evil, even in its central characters. And so rather than giving us goodies and baddies and a thick line dividing them, a technique that has admittedly worked wonders for any number of cop shows, The Riches plays in the grey area, carefully creating a unique moral universe, and then inviting us in to share it.

Initially, we’re disoriented. These characters don’t seem at all empathetic. Mother of three Dahlia Malloy (Minnie Driver) is an ex-con with a crushing addiction to cough syrup and heroin. And Man of the house Wayne Malloy (Eddie Izzard in an irresistibly charismatic performance dripping with presence and machismo and without the slightest hint of his trademark camp) is a shameless thief and swindler with a taste for young blondes.

Why, then, do we empathise with them? Because within the confines of their world, the world we’re lucky enough to be guests in, they’re trying their best. Wayne’s doing everything he can to ensure his family’s security, and Dahlia’s working desperately to kick her addictions so she can be a better mother to her children.

That is the great skill of The Riches. Once we understand its world, we see that the characters that at first seemed horribly grotesque are really just like us. So how can we not love them?