The writer reinvents the Wall

For a particular kind of thriller writer the fall of the Berlin Wall must have been the imaginative equivalent of shutting down a major steelworks - the frisson factory was in the hands of the receivers and the workers had to think about retraining in computers or service industries. Dave Pirie's Black Easter (BBC2) offers one solution to the trauma of sudden redundancy - reinvent the Wall by other means. In the near future then, the Iron Curtain has been replaced by The Strip, an immigrant exclusion zone guarded by advanced electronics and holding at bay the Muslim refugees of Eastern European civil war. On this side, a paranoid, bureaucratic state; on the other, Brueghel with neon and computer porn; in between, the old, sweet terror of crossing a border with a foreign body in the boot of the car.

Trevor Eve, fresh from moustache-twirling in The Politician's Wife, plays a shop-soiled German detective lumbered by his superior with one of those messy cases indispensable to political thrillers - a nurse ritually murdered and then helpfully autographed - the Arabic text daubed above her corpse reads "We are crossing". Naturally, Eve's character doesn't settle for what his bosses want - the first available gastarbeiter without a decent alibi. Instead, he uncovers the truth - a genocidal plot designed to increase the border police's budget and offer a final solution to the refugee problem. Black Easter was thoroughly imagined and achieved a real sense of apprehensive dread in its closing minutes. Its imagined world wasn't entirely consistent - the border police have a marvellous new- fangled gizmo that can scan your car for contraband but have conveniently neglected to fit old-fangled thermal image viewers to their helicopters. That's easily forgiven, though, for the shrewd identification of a new pressure point in our imaginations and a final scene of bleak insinuation - the survivors stagger onto a German autobahn and try, without success, to stop the indifferent flow of headlights, comfortable citizens turning a blind eye to the pleading figures by the side of the road. "They will see us... they will stop," says the heroine. You feel tense, but whether it's future or present is less clear.

Strange Landscapes (BBC2), Christopher Frayling's instructive account of the Middle Ages, has now reached its second episode and I'm still not sure quite what it's up to. Instruction, undoubtedly. Most people will have learnt things they didn't know about cathedral building and church politics from these first two programmes. But it isn't at all clear whether this information is seen to be filling a void - a general ignorance of the period - or correcting false impressions. Historical analogy is one of the problems - when Frayling points out the picture of a shoemaker in one of the Chartres windows and makes a jokey comment about "sponsorship of the arts" (it was paid for by the shoemakers' guild) the mind runs on - ah yes, the Reebok Rose Window, you think. Of course, the cathedrals were huge tourist attractions, indivisibly connected to the commercial success of the towns that surround them. It feels, for a moment, like an illuminating analogy. But a successful analogy can either be an ingenious way of bridging the immense gap that divides us from a medieval worshipper, or an indication that the gap was never that great in the first place. There's no easy way of knowing which it is, particularly if your narrator is given to rhetorical anachronism anyway - "it was a case of 'May the force be with you rather than against you'," Frayling said, discussing Chartres' use of butressing; the great medieval cathedrals were "machines for worshipping in". It's possible that Star Wars and Le Corbusier would help us to understand the mind of a cathedral builder, but I think the argument needs to be a bit more explicit than this.