Then she was out and locking the door behind her.

Back in the passage now… and quietly past that open door. Nobody seemed to take any notice. She locked the front door, and the house was fast, as it had been on the night of the murder.

She returned to the sittingroom, and found she had been so quick that Bunter was still on the steps by the fireplace, searching the dark beams with a pocket-torch.

‘A cup-hook, my lord, painted black and screwed into the beam.’

‘Ah!’ Peter measured the distance with his eye, from the hook to the cabinet and back again. Harriet held out the keys to him and he pocketed them absent-mindedly without so much as a nod.

‘Proof,’ he said. ‘Proof of something at last. But-where is the-?’

The vicar, who seemed to have been putting two and two carefully together in his mind, cleared his throat:

‘Do I understand,’ he said, ‘that you have discovered a what they call a clue to the mystery?’

‘No,’ said Peter. ‘We’re looking for that. The clue. Ariadne’s clue of thread-the little ball of twine to thread the labyrinth-the-yes, twine. Who said twine? Puffett, by jove! He’s our man!’

‘Tom Puffett!’ exclaimed the vicar. ‘Oh, I should not like to think that Puffett-’

‘Fetch him here,’ said Peter.

Bunter was off the steps before he spoke. ‘Yes, my lord,’ he said, and was gone like lightning. Harriet’s eye fell on the chain, which lay, where Bunter had left it. on top of the cabinet. She picked it up and the clink of the links caught Peter’s ear.

‘Best get rid of that,’ he said. ‘Give it me.’ He scanned the room for a hiding-place-then, with a sort of chuckle, made for the chimney.

‘We’ll put it back where it came from,’ he said, as he dived under the cowl. ‘Safe bind, safe find, as Puffett is fond of observing.’ He emerged again, dusting his hands.

‘There’s a ledge, I suppose,’ said Harriet.

‘Yes. The gun dislodged the chain. If Noakes had kept his chimneys swept his murderer might have been safe. What’s that, padre, about doing evil that good may come?’

Mr Goodacre was spared discussion of this doctrinal point by the arrival of Mr Puffett with Bunter at his elbow.

‘Did you want me, my lord?’

‘Yes, Puffett. When you were clearing up this room on Wednesday morning after we’d loosened the soot, do you remember picking up a bit of string from the floor?’

‘String?’ said Mr Puffett. ‘If it’s string you’re looking for, I reckon you’ve come to the right place for it. When I sees a bit o’ string, my lord, I picks it up and puts it away, ’andy when wanted.’ He pulled up his sweaters with a grunt and began to produce rolls of string from his pockets as a conjuror produces coloured paper. ‘There’s all sorts ’ere, you can take your choice. As I says to Frank Crutchley, safe bind, safe bind, I says…’

‘That was about a piece of string, wasn’t it?’

‘That’s right,’ said Mr Puffett, extracting with some difficulty a thick piece of small-cord. ‘I picks up a piece of string off this very floor, and I says to him-alloodin’ to that there forty pound of his-I says to him-’

‘I thought I saw you pick some up. I suppose you can’t tell by this time which piece it was?’

‘Oh!’ said Mr Puffett, enlightened. ‘I get you now, me lord. You was wantin’ that pertickler bit o’ string. Well, now, I dunno as I could rightly say which was that identical piece of string. Not the string, I couldn’t. Not but what it was a good bit of string, too-a good thick piece, reckon it might be a yard long without knots. But whether it was this piece now, or that piece I wouldn’t pretend to say.’

‘A yard long?’ said Peter. ‘It must have been more than that.’

‘No,’ said Mr Puffett. ‘Not the string-well, it might a-been four foot, not more. There was a rare good bit o’ black fishin’-line, mebbe twenty feet or so-but it’s string you’re lookin’ for.’

‘I made a mistake.’ said Peter. ‘I ought, of course, to have said fishing-line. Naturally, it would be fishing-line. And black. It had to be. Have you got that on you?’

‘Oh!’ said Mr Puffett, ‘if it’s fishin’-line you’re after, w’y didn’t you say so? Safe bind-’

‘Thank you,’ said Peter. He whipped the roll of black line deftly from the sweep’s slow fingers. ‘Yes. That’s it. That would hold a twenty-pound salmon. And I’ll bet you there’s a sinker at each end. I thought so-yes.’

He threaded one end of the line through one of the rings at the lip of the pot brought the two ends with their sinkers together and handed them to Bunter, who took them without a word, mounted the steps and passed the double line over the hook in the ceiling.

‘Oh!’ said Harriet. ‘I see now. Peter, how horrible!’

‘Haul up,’ said Peter, unheeding. ‘Take care you don’t foul the line.’

Bunter hauled on the line, grunting a little as it cut into his fingers. The pot steadied from below by Peter’s outstretched hand, stirred, lifted, moved up and away out of his reach, rising in a great semicircle at the end of the iron chain.

‘It’s all right,’ said Peter. “The plant won’t fall out. It’s a dead tight fit, as you know. Haul steady.’

He went to take the slack of the line as it came down over the hook. The pot now lay level, strung out flat below the rafters, the cactus emerging sideways, so that it looked in the dimness like a monstrous hermit crab clawing out greedily from its shell.

The vicar, peering up at it, ventured a remonstrance.

‘Pray, be careful, my man. If that thing was to slip and come down it might easily kill somebody.’

‘Very easily,’ said Peter. ‘That’s what I was thinking.’ He walked backwards towards the radio cabinet, keeping the double string taut in his hand.

‘It must weigh getting on for fourteen pound,’ said Bunter.

‘I can feel it,’ said Peter, grimly. ‘How did you come not to notice its weight when you and Kirk were examining it? It’s been loaded with something-lead shot from the feel of it. This must have been planned some time ago.’

‘So that,’ said Harriet, ‘is how a woman could have broken a tall man’s head. A woman with strong hands.’

‘Or anybody,’ said Peter, ‘who didn’t happen to be there s at the time. Anyone with a cast-iron alibi. God makes power, padre, and man makes engines.’

He brought the two ends of the line to the edge of the cabinet, to which they reached exactly. He lifted the lid and slipped them under; then brought the lid down upon them. The spring catch stood up to the strain, and the sinkers held firm against the flange, though Harriet noticed that the pull of the heavy pot had raised the near side of the cabinet slightly from the ground. But it could not lift far; since its feet were jammed close against the end of the settle, over which the thin black line stretched taut and nearly invisible to the hook in the beam.

A sharp knock on the window made them all start. Kirk and Sellon stood outside, beckoning excitedly. Peter walked quickly across and opened the lattice, while Bunter came down from the steps, folded them and set them quietly back against the wall.

‘Yes?’ said Peter.

‘My lord!’ Sellon’s voice was quick and eager. ‘My lord, I never told you no lie. You can see the clock from the window. Mr Kirk. he’s just told me-’

‘That’s right,’ said Kirk. ‘Half-past twelve, plain as a pike-staff… Hullo!’ he added, able to see better now that the window was open. ‘They’ve took the cactus down.’

‘No, they haven’t,’ said Peter. ‘The cactus is still there. You’d better come along in. The front door’s locked. Take the keys and lock it again behind you… It’s all right.’ he added, speaking into Kirk’s ear. ‘But come in quietly-you may have to make an arrest.’

The two policemen vanished with surprising speed.

Mr Puffett, who had been scratching his head in a contemplative manner, accosted Peter.

‘That’s an orkerd-looking arrangement of yours, me lord. Are you dead sure it won’t come down?’