The Missing, BBC - TV review: A hushed-up paedophile ring in government? This unmissable thriller is worryingly prescient

It's the minor mysteries that make this drama starring James Nesbitt so gripping

Six episodes into eight-part thriller The Missing and we're beginning to understand every grey hair on the head of present-day Tony Hughes (James Nesbitt). There's one from the breakdown of his marriage, one from the guilty remembrance of what happened on the boat and at least two from Karl Sieg (Johan Leysen), last night's stand-out villain.

We were off on a day trip to Belgium, but not to sample the moules-frites, judging by that grim look on the face of Inspector Julien Baptiste (Tchéky Kary). He and Tony were following up on a fresh lead. Did Sieg, former associate of Romanian gang the Caid de Cité, know anything useful about the disappearance of Tony's son? And would he tell them even if he did?

The true mark of quality in a drama series like this one isn't the central characters – although Nesbitt and Karyo are both reliably good – it's ones who stop by only for an episode or two. The Missing is full of such well-drawn, well-acted incidental players, all of whom contain a minor mystery of their own. In this episode, it was Sieg, eventually found tending bar in a neon-lit, Brussels dive, where a fat bloke crooned Jacques Brel songs from the stage. Seig's cheerful amorality offset the pair's desperation a treat. "You want money?" asked Tony, against Baptiste's better judgement. "Like a fish needs water, my friend," came the reply.

Not all villains lurk in dimly lit drinking dens, however. Some are found issuing instructions from the mayor's office, as liaison officer Mark (Jason Flemyng) discovered in the 2006 timeline. "Ian Garrett is a friend to the department," explained local police officer Laurence, when the investigation into Garrett's crimes came to a sudden halt. "Dig too deep and they're scared we'll find skeletons."

To think, only a year ago the suggestion of a hushed-up paedophile conspiracy in government might have seemed like far-fetched TV nonsense.

While some characters fell under suspicion, others grew more sympathetic. Emily's insistence on "moving on" from the abduction of her son seems less callous, now we know how necessary her self-preservation is, and even Seig had one redeeming moment. He chose not to wipe Oliver's drawing from that basement wall, thus preserving the single most important clue in the investigation: "I left it there because I didn't think it right that he should disappear completely."