Solving the mystery that is Reichenbach Falls might take all the ingenuity of Sherlock Holmes - which is just as well as his creator features in the story.

Everything about Reichenbach Falls, including the title, is part of a game where nothing is quite what it seems. If you're clever enough to pay attention and follow the clues, the penny might drop before the final credits, which are part of the joke too.

The makers want me to keep the twist in the tale secret. So I won't reveal whodunit - if, in fact, anything was "dun" by anyone. Besides, getting a grip on the plot was as tricky as picking up an eel coated in grease.

Detective Inspector Buchan (Alex Newman) is first seen having a three-monthly undercover operation rumbled, leading to the shooting of a colleague and the escape of the chief villain known as The Monkey.

Then there's Jack Harvey (Alistair MacKenzie), a successful writer of thrillers set in Edinburgh. He's married to Buchan's former love, Clara (Laura Fraser), with the result that the two hate each other. "You're really over her, aren't you?", someone says sarcastically to Buchan on seeing that a wall in his flat is plastered with pictures of Clara.

"We have to go back to Sherlock bloody Holmes," says Buchan in his voiceover, without realising that the Baker Street sleuth's creator Sir Arthur Conan Doyle will turn up in ghostly form from time to time to point him in the right direction.

As you can tell, this is hardly a run-of-the-mill cop drama. It's based on an idea by top thriller writer Ian Rankin and a certain amount of fun is had at his own expense in the character of Harvey.

The glorious views of Edinburgh - whose cultural and architectural delights earned it the label "Athens of the North", we're reminded - and the city's inclusion as one of the characters in the story also stem from Rankin's love of the place.

Alex Newman adopts a suitably befuddled air as Buchan (I didn't count but there may well have been 39 steps leading to his upstairs flat).

"I don't get this," he says, echoing many a viewer's own feelings at the spirited appearance of Richard Wilson as Conan Doyle. "You can call me Arthur," he tells Buchan, as if talking to a dead man is a commonplace occurrence.

Tony Robinson is exploring splendid architecture, not in Edinburgh but Ramsgate, in a Time Team Special. There's no hanging around in fields, digging in muddy trenches or examining dirt-encrusted finds this time.

This is a visiting-posh-places job as he views the work of Augustus Pugin, the man responsible in the mid-19th Century for a style of architecture known as Gothic Revival.

He was certainly a busy chap, designing and building six cathedrals, 40 churches and numerous private houses in a 15-year period. Perhaps it was overwork that caused his death when he was only 40.

Wallpaper, candlesticks, chairs and stained glass were all among his output. Perhaps he's most famous for the expensive wallpaper put up in the Lord Chancellor's office that caused a rumpus a few years back.

His influences included York Minster, a building that took his breath away, although Salisbury Cathedral made even more of an impact. Away from work, Pugin converted to Catholicism and built his own private chapel in his home.

Robinson dutifully takes us through Pugin's life and work, although the latter was more colourful than the former.

He shows us round his home, The Grange in Ramsgate, which was threatend with destruction in 2004 until the Landmark Trust stepped in to restore it. What Pugin did there helped shape the way we live now.

The programme isn't without criticism of Pugin's work. He was a perfectionist who sometimes overdid things, says Robinson. "The wealth of colour is too much for my taste - it's genius working overtime".