Dirk Gently, BBC4, Thursday<br/>The Apprentice, BBC1, Wednesday

Very loosely based on Dirk Gently's Holistic Detective Agency by Douglas (Hitchhiker's Guide) Adams, but without the planet hopping and unicorns, Dirk Gently began with a scene of teatime, flowery china and an old lady's lost cat.

The following hour brought us burglary, time travel, drugged beverages, hypnosis, computer hacking, an exploding warehouse, a double murder and the search for a missing billionaire. The conceit so cleverly expanded in this hour-long adaptation is that all the random events and apparent coincidences are linked by the laws of quantum mechanics – evidence of what Gently described (several times) as "the fundamental interconnectedness of all things".

Douglas Adams was a genius at pulling the mundane and the intergalactic into absurd but hilarious harmony, and some of that spirit survived Howard Overman's adaptation. In Gently's world, an obsessed suitor responds to his girlfriend's dread words, "You had your chance and you blew it. You're too late," by building a time machine, years later, to give himself a second crack at winning her.

The plot unfolded in a series of droll encounters, underlined by visual gags, don't-blink flashbacks, diagrams and snappy camerawork as our hero investigated clues and leads with his slow-on-the-uptake associate, MacDuff. It was a lovely bonus that both men weren't to be trusted for a second. From the start we knew that Gently was a hopeless, money-grabbing conman, while MacDuff was first seen burgling his girlfriend's house to steal a laptop, to which he'd sent a terminally ill-advised email.

Given the talent and style on display, it should have been a scream. In fact it all seemed a little moth-eaten. Though set in the modern day, it was staggeringly old-fashioned, with cosy 1950s sets straight from Wallace and Gromit, and a jazz soundtrack straight from the Carry On films. Many of the jokes were ancient – the snapping of a rubber glove for a per rectum examination, Dirk's non-starting car, a You-are-feeling-sleepy hypnotism scene. It felt as if Overman had tried to graft Douglas Adams's essentially 1980s humour on to a modern TV idiom and produced a mis-shapen hybrid.

You could overlook these faults, however, for the joy of Stephen Mangan's performance as the titular gumshoe. With his alarmed-spaniel eyes and jutting-jawed stroppiness, his geography teacher elbow-patches and Medusan hair, he radiates mess. A striver after connectedness, he's a walking embodiment of chaos. His ineptness as a sleuth provided some fine comic moments. When sinister old Mrs Jordan was asked if she knew a murder victim, we registered the momentary look of panic on her face – but Dirk was too busy fishing half a chocolate digestive out of his tea. I wish we could see more of Mr Mangan, in Dirk Gently II or anything else.

In The Apprentice, it was Reality Check time as the remaining five self-deluded egomaniacs, sorry, contestants were interviewed by four of Lord Sugar's beady-eyed associates. Awkward questions were asked, and dismaying judgements passed; it was as if a fire crew had invaded a kindergarten where a game of "shops" was in progress, and hosed down the participants with freezing water. Joanna, the contract-cleaning entrepreneur, failed to identify which companies Sugar owned (she seemed unfamiliar with the name Amstrad) and was told that her own company had "come to the end of the road". She looked understandably aghast. Chris, the posh one, was teased for claiming he was "revered as one of the outstanding theology students of my year" and told he was "a quitter". Jamie, the charming dealer in Cyprus real estate, when asked whether his company existed, stammered that he "did 99 per cent of the work" and was about to break with his partner. In a bowel-freezing exchange, Stuart "the Brand" Baggs came before a terrifying inquisitor called Claude. "What on earth are you talking about?" said Claude. "You're not a brand." Stuart mildly pointed out he was a big fish in a small pond. "You're not a big fish," yelled Claude. "You're not even a fish!"

The Brand was duly fired, after they found he'd massaged his CV. The words, "You're full of shit" were passed down by His Lordship like a pontifical judgement. Chris and the cool blonde, Stella, are in this week's final. I'm amazed by The Apprentice. Who'd have thought, 10 years ago, that an hour of business people discussing management virtues and vices could make for nail-biting drama?