"Okay, then. We're on our way… Forgive me for being obtuse, April — but I'm afraid I still can't quite see why we're on our way, just the same. On this particular deal, I mean. What good is it going to do us?"

She laid a hand on his arm. "Look, Mark," she said; "we're floating around in a bit of a mess, aren't we, not knowing what's a police job, what's our job, and who's involved in which?"

"Too true."

"All we know is that everybody seems to be involved in something. And the easiest way to sort out our own pigeons from those of the police — if indeed there is any difference — is to find out for ourselves precisely what everybody really is up to."

"Yes, I suppose so."

"Well, we happen to have a big advantage over the police here. They have to have a warrant before they search anything. And they have to have a good reason before they get a warrant. Because we work undercover, we can get in without a warrant—"

"Illegally."

"— illegally, as you say. But it's a much quicker way of finding things out, I think you'll agree!"

"Oh, the point is taken," Slate said carelessly, "and all the principles accepted. It's just that I don't see this particular one, as I say."

"The Bosustows, you mean?"

Slate nodded.

"Because they are obstructing the police, for one thing. According to your friend Curnow, the old man practically tries to stop them coming in every time they want to ask a question, doesn't he?"

"That's true; he does. I've seen him being pretty unpleasant to Curnow myself."

"And he never gives a straight answer, never volunteers anything, and only talks at all if it's dragged from him?"

Again the agent murmured an affirmative.

"Well, why?" April demanded. "You'd think he'd be only too glad to have the thing cleared up as speedily as possible. After all, she was murdered on his property, while she was working for him — and it can't be all that good for business having a permanent boy in blue at the gate, I imagine!"

"True again. And I suppose the same thing goes for your other bird?"

"The son? Certainly... We've got to find out what they're up to — and if it's connected with us in any way. At the moment we have a minor agent killed, possibly in the course of duty, possibly not; we have the possibility that she had discovered something going on at the DEWS station behind the town; we have the possibility that she was part of a jealous triangle — the other two members being the local squire and a stone worker. In the cast also are suspicious families, intruders in the night, people who roll rocks on cars, and at least one — possibly two — murderers. To say nothing of complaisant wives striking up acquaintances with us and then joining a queue of boys seeking to buy a non-existent pixie!"

"To all of which must be added another possibility," said Mark. "That the said queue was in some way connected with a dope ring. It certainly looks as though asking for a black Porphyry pixie was, as you thought, a code. And the lucky winner was handed, not a pixie, but a black Porphyry light house — a secret compartment in which was filled with a mysterious white powder."

"Well, there you are!" the girl said triumphantly. "There may be more than one mystery to solve here, and the sooner we start our process of elimination, the better... You did send the powder to an analyst, by the way?"

"Yes. I had to send it to a firm in Truro. There didn't seem anyone suitable nearer. These people work for some of the big private investigation agencies and they're on the books of London HQ as being okay. I put it on the train at Helston just before lunch."

"Good… Look, here's the hut the old man uses as a kind of general office. I saw the wife of the brother who was murdered staggering in here laden with books today — the big, brassy one, isn't it? — and if, as you say, she's the one who keeps the accounts, then we should be able to find out something or other about something in here!"

Mark Slate drew a rectangular bakelite box from the pocket of his raincoat, moistened the four tiny suction cups at the corners, and clamped it firmly to the door of the hut over the lock — which was surprisingly robust for so flimsy a structure. He crouched down, switched on the pencil beam of a fountain-pen torch for the briefest of moments, and manipulated a pair of knobs with milled edges. A few seconds later, there was a distinctive, heavy click above the pelting of the rain. He stood up. "That's that one," he said. "There's only the ordinary mortice now — I think I'll borrow your twirls, if you have 'em on you, lovey."

April handed him a bunch of skeleton keys. After the third attempt, he gave a grunt of satisfaction and twisted the handle. The door swung inwards.

The hut smelled of linseed oil and old books. It was stuffy and airless and the rain drummed exasperatingly on the asphalt roof. In the thin ray of light from the torch, they saw that it was furnished only with a scarred table, a swivelling office chair with the stuffing showing through a hole in the seat, a poorly made shelf full of reference books, and three steel filing cabinets, all of which were locked.

"Oh, well — here we go again," Slate murmured, taking the bakelite device from his pocket once more. "Thank goodness this electronic monster leaves this kind of lock so that it automatically springs shut again when you close the drawer! There's nothing I hate more than going round un-picking locks that I've just opened, when I leave a place."

Each of the cabinets had four drawers, and most of them — Mark saw as soon as he had opened them successfully — were full of files dealing with the normal day-to-day affairs of the circus: invoices, bills and receipts for goods purchased; cancelled cheques; wages slips; details of employment; insurance papers; Pay-As-You-Earn documents, and so on. One drawer, however — the bottom one in the cabinet furthest from the door — seemed to interest him especially. After a glance at the ledger nearest the front, he pulled out all the files and books inside and carried them over to the table.

"Found something?" April asked. "You're the one with the diploma in bookkeeping. So if you have, you're on your own, mate!"

"Books of the circus," he explained absently, subsiding into the old chair and shading the tiny flashlight with one cupped hand. "The kind that get audited and shown to Her Majesty's Inspector of Taxes... if you're unlucky. And there seem to be two sets, what's more. The plot, as they say, thickens."

For some time, he worked in silence, opening ledgers and running a finger down columns of figures, rifling through pages in another book and comparing them with the entries there, jotting down an occasional note on a scrap of paper he had taken from his own pocket. April sat on the window ledge and watched the shaded beam of the light race up and down the ruled pages. From time to time, her companion gave a grunt — though whether it was of astonishment or of satisfaction she couldn't tell. Once he gave a low, long whistle — and once he erupted into a short bark of laughter, instantly stifled. Finally he shut the last book with a snap, leaned back in the creaking chair, swivelled himself round to face her and stretched his arms above his head.

"Well, double-entry bookkeeping does have its advantages," he said; "especially when there are two different sets of books as well! But I've never seen anything quite like this before. Either the woman's mad, or she's a near-genius!"