'But if this man Sir Ronald is paying her to find out about Mark, why cannot I pay her to stop finding out?'

Then Hugo's voice, amused, a little contemptuous:

'Darling Isabelle, when will you learn that not everyone can be bought?'

'She can't, anyway. I like her.'

It was Sophie speaking. Her brother replied:

'We all like her. The question is, how do we get rid of her?'

Then for a few minutes there was a murmur of voices, words undistinguishable, broken by Isabelle.

'It is not, I think, a suitable job for a woman.'

There was the sound of a chair scraping against the floor, a shuffle of feet. Cordelia darted guiltily back into the bathroom and turned off the tap. She recalled Bernie's complacent admonition when she had asked whether they needed accept a divorce case.

'You can't do our job, partner, and be a gentleman.' She stood watching at the half-open door. Hugo and Isabelle were leaving. She waited until she heard the front door close and the car drive away. Then she went down to the parlour. Sophie and Davie were together, unpacking a large carrier bag of groceries. Sophie smiled and said:

'Isabelle has a party tonight. She has a house quite close to here in Panton Street. Mark's tutor, Edward Horsfall, will probably be there and we thought it might be useful for you to talk to him about Mark. The party's at eight o'clock but you can call for us here. Just now we're packing a picnic; we thought we'd take a punt on the river for an hour or so. Do come if you'd like to. It's really much the pleasantest way of seeing Cambridge.'

*

Afterwards, Cordelia remembered the river picnic as a series of brief but intensely clear pictures, moments in which sight and sense fused and time seemed momentarily arrested while the sunlit image was impressed on her mind. Sunlight sparkling on the river and gilding the hairs of Davie's chest and forearms; the flesh of his strong upper arms speckled like an egg; Sophie lifting her arm to wipe the sweat from her brow as she rested between thrusts of the punt pole; green-black weeds dragged by the pole from mysterious depths to writhe sinuously below the surface; a bright duck cocking its white tail before disappearing in a flurry of green water. When they had rocked under Silver Street Bridge a friend of Sophie's swam alongside, sleek and snout-nosed like an otter, his black hair lying like blades across his cheeks. He rested his hands on the punt and opened his mouth to be fed chunks of sandwiches by a protesting Sophie. The punts and canoes scraped and jostled each other in the turbulence of white water racing under the bridge. The air rang with laughing voices and the green banks were peopled with half-naked bodies lying supine, with their faces to the sun.

Davie punted until they reached the higher level of the river and Cordelia and Sophie stretched out on the cushions at opposite ends of the punt. Thus distanced it was impossible to carry on a private conversation; Cordelia guessed that this was precisely what Sophie had planned. From time to time, she would call out snatches of information as if to emphasize that the outing was strictly educational.

'That wedding cake is John's – we're just passing under Clare bridge, one of the prettiest, I think. Thomas Grumbald built it in 1639. They say he was only paid three shillings for the design. You know that view, of course; it's a good view of Queen's, though.'

Cordelia's courage failed her at the thought of interrupting this desultory tourist's chat with the brutal demand:

'Did you and your brother kill your lover?'

Here, rocking gently on the sunlit river, the question seemed both indecent and absurd. She was in danger of being lulled into a gentle acceptance of defeat; viewing all her suspicions as a neurotic hankering after drama and notoriety, a need to justify her fee to Sir Ronald. She believed that Mark Callender had been murdered because she wanted to believe it. She had identified with him, with his solitariness, his self-sufficiency, his alienation from his father, his lonely childhood. She had even – most dangerous presumption of all – come to see herself as his avenger. When Sophie took over the pole, just past the Garden House Hotel, and Davie edged his way along the gently rocking punt and stretched himself out beside her, she knew that she wouldn't be able to mention Mark's name. It was out of no more than a vague, unintrusive curiosity that she found herself asking:

'Is Sir Ronald Callender a good scientist?' Davie took up a short paddle and began lazily to stir the shining water.

'His science is perfectly respectable, as my dear colleagues would say. Rather more than respectable, in fact. At present the lab is working on ways of expanding the use of biological monitors to assess pollution of the sea and estuaries; that means routine surveys of plants and animals which might serve as indicators. And they did some very useful preliminary work last year on the degradation of plastics. R.C. isn't so hot himself, but then you can't expect much original science from the over fifties. But he's a great spotter of talent and he certainly knows how to run a team if you fancy that dedicated, one for all, band of brothers approach; I don't. They even publish their papers as the Callender Research Laboratory, not under individual names. That wouldn't do for me. When I publish, it's strictly for the glory of David Forbes Stevens and, incidentally, for the gratification of Sophie. The Tillings like success.'

'Was that why you didn't want to stay on when he offered you a job?'

'That among other reasons. He pays too generously and he asks too much. I don't like being bought and I've a strong objection to dressing up every night in a dinner-jacket like a performing monkey in a zoo. I'm a molecular biologist. I'm not looking for the holy grail. Dad and mum brought me up as a Methodist and I don't see why I should chuck a perfectly good religion which served me very well for twelve years just to put the great scientific principle of Ronald Callender in its place. I distrust these sacerdotal scientists. It's a bloody wonder that little lot at Garforth House aren't genuflecting three times a day in the direction of the Cavendish.'

'And what about Lunn? How does he fit in?'

'Oh, that's boy's a bloody wonder! Ronald Callender found him in a children's home when he was fifteen – don't ask me how – and trained him to be a lab assistant. You couldn't find a better. There isn't an instrument made which Chris Lunn can't learn to understand and care for. He's developed one or two himself and Callender has had them patented. If anyone in that lab is indispensable it's probably Lunn. Certainly Ronald Callender cares a damn sight more for him than he did for his son. And Lunn, as you might guess, regards R.C. as God Almighty, which is very gratifying for them both. It's extraordinary really, all that violence which used to be expressed in street fights and coshing old ladies, harnessed to the service of science. You've got to hand it to Callender. He certainly knows how to pick his slaves.'

'And is Miss Learning a slave?'

'Well, I wouldn't knowjust what Eliza Learning is. She's responsible for the business management and, like Lunn, she's probably indispensable. Lunn and she seem to have a love-hate relationship, or, perhaps, a hate-hate relationship. I'm not very clever at detecting these psychological nuances.'

'But how on earth does Sir Ronald pay for it all?'

'Well that's the thousand dollar question, isn't it? It's rumoured that most of the money came from his wife and that he and Elizabeth Learning between them invested it rather cleverly. They certainly needed to. And then he gets a certain amount from contract work. Even so, it's an expensive hobby. While I was there they were saying that the Wolvington Trust were getting interested. If they come up with something big – and I gather it's below their dignity to come up with something small – then most of Ronald Callender's troubles should be over. Mark's death must have hit him. Mark was due to come into a pretty substantial fortune in four years' time and he told Sophie that he intended to hand most of it over to Dad.'