RADIO / Elementary, my dear: Robert Hanks reviews The Memoirs of Sherlock Holmes, The Virgin in the Ice and Run Man Run

It should have been obvious from the beginning, of course. The secretive habits, the indifference - even aversion - to women, the intense masculine friendships, the flamboyant taste in headgear: the clues were there if you looked for them. And as the great detective said himself in 'The Greek Interpreter' - last week's episode of The Memoirs of Sherlock Holmes (Radio 4, Wednesday) - 'Art in the blood takes the strangest forms.'

A faint homoerotic tinge can be discerned in Holmes's relationship with Watson if you look at it in the right light: but Clive Merrison's performance magnifies and distorts it into high camp. As the BBC's projected complete cycle comes up to the half-way stage - it reaches a natural caesura next week when Holmes travels to the Reichenbach Falls to meet Moriarty - Merrison and his Watson, Michael Williams, are showing mild signs of strain. This Holmes, always a touch temperamental, now teases, bullies and flirts with a weary, henpecked Watson who musters the odd flash of retaliatory sarcasm, but mostly sinks into a submissiveness bordering on the masochistic.

Gerry Jones's dramatisation of 'The Greek Interpreter' added new dimensions to the relationship. This is the story in which we meet Mycroft, Sherlock's brother and his superior in observation. Being too lazy to take any active part in the matter, he asks Sherlock's help in solving a mystery that afflicts his upstairs neighbour, the interpreter of the title. Aside from some necessary fiddling with Doyle's over-formal dialogue, one of Jones's innovations is to have Mycroft call his brother 'My dear' (not 'My dear Sherlock', just 'My dear') - once or twice, Sherlock throws the familiarity back at him rather acidly. This Holmes, too, has a passion for picnics in the park ('With a dear friend,' he tells Watson), and turns sulky and childish if Watson tries to bring up serious business. Such behaviour is not strictly according to Doyle; but this Holmes is highly enterprising, and the cycle is still deeply entertaining.

How different from Brother Cadfael. For a start, Ellis Peters' medieval monk-cum-amateur sleuth is robustly heterosexual: 'Love shared is no sin,' he said last week in The Virgin in the Ice (Radio 4, Thursday), reminiscing fondly about a widow he used to know in the Holy Lands.

The talents involved in this serialisation are considerable: Sir Michael Hordern speaks the narration and Philip Madoc plays Cadfael, while Bert Coules, the adapter, has been responsible for some of the best of the Holmes dramatisations. But they can't dispel the sense that this is cod history: the language is toned down Ivanhoe ('I will so say,' a peasant declares, agreeing to pass on a message), and Cadfael seems untouched by any of those theological prejudices you might expect from a medieval monk - as the remark about the widow makes clear, he suffers no Augustinian anxieties about the flesh, and God seems a rather remote influence on his life. If any historical period is represented by his benignly liberal outlook, it's the 1960s, not the 1130s.

Cadfael is another in a long run of fictional detectives endowed with distinguishing idiosyncrasies. Others have been insurance men, or Roman Catholic priests, or peers of the realm, or jockeys, or portrait painters, or dons, or Belgians; or they have some vaguely eccentric hobby, like growing roses, or orchids, or writing poetry or solving crosswords. Cadfael's shtick is that he lives in the 12th century. Apart from that, he is a colourless character - for someone nominally concerned with prospects in the next world, he remains oddly earthbound; and, most dispiritingly, he is utterly without humour.

He loses out in that respect to the characters of Run Man Run (Radio 5, Monday), a convoluted and bloody novel by Chester Himes now adapted in four parts. In the first episode, set around four o'clock one morning between Christmas and New Year 1959, Detective Walker (Bill Nighy, cramping his vowels rather uncomfortably into something approaching a New York accent) turns up at a diner, drunk and angry and, after some crosstalk, shoots one of the night-porters for stealing his car. Realising his mistake, he tries to clear up the mess by killing the other porters; he gets one, but is interrupted before he can do more than severely wound the other.

Even muted by a silencer, the shooting comes across brutally in Chris Wallis's production. But what's more striking than the cartoon violence and the racism - Walker is white, his victims are black - is that the author allows you to sympathise with Walker's frustration and cynicism, and to admire the wit of his hastily improvised explanation of how he came to be surrounded by corpses. This, you can't help feeling, is what a murder ought to be.