The Event, Channel 4, Friday<br/>The Taking of Prince Harry, Channel 4, Thursday

Channel 4's latest US import, portentously titled political thriller / sci-fi mash-up The Event, begins plausibly enough.

Perky twentysomething Leila waves her parents goodbye before heading off on a cruise with lantern-jawed boyfriend Sean. Wait. A young couple going on a cruise? I know the liners have been working hard to dispel the greys-and-gays stereotype, but really? Still, it's easily the show's most credible proposition.

No surprise that it's not all sunshine and cocktails. Seven days later Leila has vanished and nice guy Sean appears to be hijacking a plane. I'm still not clear how we got from A to B (nothing is mind-bendingly difficult, it's just relayed via a dizzying chain of flashbacks), but it can all be traced back to a plane crash in Alaska half a century ago. The human-looking survivors picked up by the US military were found to be (groan!) extraterrestrials who have been held secretly by the CIA ever since.

Now, America's recently elected black president (one of many cheap stabs at relevance) wants to liberate the ETs and tell the world. It never happens, though, because moments before his press conference kicks off, the plane that Sean is attempting to re-route nosedives towards the president's residence. Suffice it to say there are a few more manoeuvres that get Sean tangled up in this (not all of which have thus far been revealed), but you get the Ordinary-Joe-caught-up-in-a-massive-conspiracy gist.

Until this point it is quite gripping – the nimble structure kept me watching, and the cast, new faces mixed with more familiar ones such as Blair Underwood and ER's Laura Innes, are good. But just as you think the Pres and his family are toast, the plane disappears in a ball of swirling light and it becomes clear that this is a show where sci-fi is less a basis for asking difficult questions than a device for fudging them. When the genre serves as a deus ex machina for tricky bits, it's hard not to feel that it's the refuge of writers incapable of devising a mystery within rational bounds.

In the US, The Event has been hyped as an inheritor of the Lost tradition, but given the latter's frustrating finale, I wonder whether people will stick with this one long enough to find out what ominous "event" the aliens are actually planning. I'll happily tune in if it's a flash-forward to a world where people are no longer making dodgy imitations of Lost.

Or how about a TV landscape without overblown "what if" documentaries? Channel 4's other televisual "event" last week, The Taking of Prince Harry, had everyone in a lather before broadcast, but the controversial premise – what might happen if Harry were kidnapped on military duty in Afghanistan – produced little that could be genuinely shocking to anyone who watches the news.

At 90 minutes it felt laboured, but had they lost the silly dramatisations of Hazza being roughed up, it might have made a passable documentary. But then we would have been deprived of gems such as the British recruit to the Taliban asking the incognito prince if "he'd been on the telly".

It threw up some interesting points – the thorny question of government policy on ransoms, for one – and there was a sensible question in all of this: should Prince Harry be allowed to return to Afghanistan if his protection puts other soldiers at risk? Since the makers didn't have the balls to stage anything but a fairytale rescue, of the kind that the recent case of Linda Norgrove reminds us doesn't exist, the question remained unanswered.