The girl took the flashlight and began looking through the negatives. The first pile were all 2.5" x 2.25", presumably taken either by the Hasselblad or the Rolleiflex. They showed a man walking along with a children's bucket and spade, a group of three giggling teenagers, several couples sheepishly smiling, and a three-generation family group on the quayside. The numbers on all of them corresponded with ordinary-sounding names and addresses in London, in the Midlands and in the North, all entered in one of the notebooks.

All the second group were 35mm negatives from the Leica. In subject matter they were subtly different. They, too, were mostly couples — but whereas the first group were all exteriors, with people obviously aware that they were being photographed, the people in the second group looked for the most part too absorbed in each other to notice the camera. And some of them were in unexpected surroundings. Two showed couples sitting over drinks on what looked like a hotel terrace; one was a telephoto lens shot of a man and a girl on a beach; another showed a military-looking man in a swimsuit holding hands with a lifeguard; the fifth, a picture taken by flash, was of a man and a woman sitting, with astonished expressions, in the back of a car. At the sixth, April paused: "But surely that's the landlord of the pub you're staying in! "she said.

"Yes it is. But the girl in the bikini with him is not Mrs. Walker. Have you checked the second series against the other notebook? "

"Not yet. I'll… Oh. They seem all to be in some sort of code."

"They are. Probably names and addresses too — with a bit of time-and-place thrown in. And perhaps an amount."

The girl looked up. "Blackmail?" she said softly.

"That's the way it looks, doesn't it? There are two separate series of photos here. The conventional seaside snapshot ones, complete with names and addresses; just enough to make a convincing cover, but not enough to make a living, I can assure you. And the second series — all of couples, and, I surmise, all of couples who ought not to be together. You know — the wrong man with the wrong wife at the wrong time. That couple so innocently sitting on the terrace, for example: he's probably supposed to be on a business trip to Glasgow, and there he is with a strange woman at the seaside. You'll notice that most of them have a calendar in shot, or a newspaper, or something by means of which, with a magnifying glass, the date could be established."

April made a grimace of disgust. "Spying on people with a miniature camera," she said. "It's about the lowest form of blackmail I can think of."

"Yes — and it certainly gives us a reason for the man to have been murdered. I guess there are as many potential murderers as there are envelopes in this second series here! And talking of motive… I wonder if Harry could have been killed by a blackmail victim — and still be tied up in our affair?"

"What do you mean?"

"Well, Sheila was involved in a triangle. One member of the triangle was married. Despite what his wife said to me personally, Sir Gerald Wright could in fact quite easily have wished to keep the friendship to himself... It brings up the possibility that Harry Bosustow was murdered by a blackmailee who was the illicit boyfriend of his future sister-in- law!"

"Oh, now really!" April protested with a laugh. "We already have genuine sabotage and espionage, genuine murder, hypothetical attempted murder, blackmail and dope rings! Surely you can't —"

The door slammed open with a crash. The young man standing there with his hair plastered to his forehead was soaked from head to foot. But the old-fashioned revolver in his hand was dry—and it was steady.

Over the steady pelting of the rain, his voice climbed the scale in near hysteria. "Who are you?" he demanded. "And just what the hell d'you think you're doing in my brother's caravan?"

CHAPTER TEN: THE JEALOUS YOUNG MAN ON THE FLYING TRAPEZE

FOR a long moment there was complete silence. April Dancer, seated at the table in the act of raising a negative, froze with her hand in mid air. Only her eyes flicked upwards, to stare steadily at the man with the gun. Mark Slate hovered by her side, slightly crouched, his hands, with the fingers extended, held away from his body. And the young roan himself stood with his feet planted apart, regarding them both with blazing eyes.

Then a sudden gust of wind outside hurled an unusually heavy scatter of raindrops on to the caravan roof; the door slammed shut again; and the tension was broken.

"All right then," the young man cried hoarsely. "Over there, both of you — up against that wall. Put up your hands…"

He advanced another pace towards the table, gesturing menacingly with the revolver. Warily, Slate inched back, his eyes never leaving the boy's face. April could sense the restraint within him, suppressing energy like a coiled spring. She herself, however, continued to sit calmly at the table. The hand holding the negative fell naturally back to the surface. Otherwise she did not move.

"I said over there," the boy repeated. "Get moving."

"You must be poor Sheila's fiance the youngest Bosustow. Ernie, isn't it?" the girl asked conversationally.

"What if I am? What is it to you? Get up!''

"Now let's not be melodramatic," April soothed. "You know perfectly well that you won't use that gun... that you can't use it..."

"I know nothing of the sort. If you don't get up and move over there, I warn you, I will use it." The boy' voice was shrill with hysteria. The gun had begun to shake slightly in his hand. As the knuckle of the forefinger whitened imperceptibly on the trigger, Mark gave an involuntary cry of alarm and warning.

"It's all right, Mark," April said quietly. "Don't worry. He won't shoot. He can't... That's a revolver from one of the sideshows. I recognised it at once. He must have been passing by, seen that there was someone here and dashed back to the booth to get it. Even if it was loaded, it only fires a kind of superior airgun pellet — but I happen to know it can't be loaded because the girl always takes the ammunition home with her. He's just bluffing, that's all."

"It is not a sideshow gun! It's loaded with... I... I'll show you..." The boy was inarticulate with fury.

"Oh, come now!" April's cool voice, laced now with asperity, cut across him. "What kind of fools do you think we are? Of course it's a sideshow pistol. Look at the plate on the butt." She raised a hand and pointed.

Involuntarily, the young man dropped his eyes to the weapon in his hand — and in that instant the steel spring that was inside Mark uncoiled..

Arrowing across the caravan with one forearm extended, he caught the boy under the chin and forced him backwards as April leaned over the desk and plucked the revolver from his hand.

Bosustow slammed back against the door, made as though to punch at Mark's face, and then dropped unexpectedly to his hands and knees and jerked at the agent's ankles. Slate came down with a crash, back-somersaulted with the momentum of his fall and regained an upright position on his own knees as the boy scrambled to his feet again.

He ran in lightly and aimed a vicious kick at Slate's face. The agent swayed back on his heels and let the shoe whistle past his chin. By the time the boy had arrested his run and turned round, Mark was on his feet, waiting.

He stood stock still as the young man feinted to the left, darted to the right and then advanced, ducking easily under a roundarm swing which was telegraphed all the way. Then, as Bosustow's impetus carried him past, he stepped aside, swivelled on one heel and planted a single, scientific, short-arm jab carrying all his weight squarely in the boy's solar plexus.