Shifting to a slightly more comfortable position in the Vultee's cockpit seat, Dave Dawson absently drummed the fingers of one hand on the side of the cockpit and stared down at the sky-blue Caribbean Sea rolling far beneath his wings. Behind him was Puerto Rico, and a considerable way ahead of him was the British-owned island of Trinidad. Several miles off the Vultee's left wing tip were the Leeward and Windward islands of the West Indies jutting up out of the blue water. High above him was a cloudless sky with a shimmering ball of gold in the center.All in all, it was a scene that would have made poets rave, and the hardest of hearts melt. However, if the truth must be known, it left Dawson cold. Not because he did not possess an eye for Nature's beauty; it was rather because, though he was looking at it, he wasn't actually seeing it. His mind was too filled with other and more personal thoughts.

The previous night he and Freddy Farmer had taken off from Bolling Field and had flown directly to the Army Air Forces base at Miami. There, after making sure, they had delivered the first of the sealed envelopes. Later they had flown on to the base at San Juan, on Puerto Rico, and delivered the second envelope. Now they were winging their way farther south to the Air Transport Command base at San Fernando on Trinidad.

"After Trinidad, Paramaribo, and Belem, and Natal," Dawson said, and scowled down at the beautiful Caribbean. "That's just the point, too. A couple of air-mail pilots, that's all we are!"

"What's that, Dave?" he heard Freddy Farmer's voice in the inter-com phones. "What are you mumbling about?"

"Mumbling?" Dawson snorted. "I was shouting with joy! I'm so excited that I can hardly keep from jumping overboard. And now that I think of it, maybe that would be a good idea!"

"Then go right ahead, old thing," the English youth in the rear pit chuckled. "Nothing I want more than for you to have your own way, you know."

"Don't look right now, but you can go fly a kite to the moon, pal!" Dawson growled. "I suppose you're enjoying this here-to-there hop in the sky?"

"Well, I have seen better piloting," Freddy came right back. "But, considering one thing and all, I'm not too fed up—yet. On the other hand, it is a bit boring. I mean—"

"You mean what?" Dave asked as Freddy let the rest hang in mid-air.

"Don't know just how to put it in words," young Farmer replied. "But—well, after that little talk with the colonel last night, I was quite steamed up, as you would say. Very mysterious, and exciting, and possibly dangerous, if you get what I mean."

"I do," Dawson grunted. "But all it is to me now is mysterious. You can have my share of the excitement and danger, if any. I'm just full of beans, though, I guess. After some of the close shaves you and I have had, routine stuff just gets me down, but quickly! But there have been two bright spots in this thing so far, thank goodness."

"Bright spots?" Freddy Farmer echoed. "Then I must have been looking the other way at the time. What do you mean?"

"At Miami and San Juan," Dawson replied. "The way those two commanding officers tried to pump us as to what the sealed envelopes contained. It was nice to look very wise and not tell them a darn thing. It was fun to see somebody else floundering around in the dark. Misery loves company. Say! Know what I hope, Freddy?"

"I wouldn't even dare guess!" the English-born air ace replied. "What do you hope?"

"That the lad we contact at San Fernando has a copper disc with numbers that add up to forty-five!" Dawson told him.

"What?" young Farmer gasped. "Forty-five? But, Dave, the number is—"

"Sure, forty-one!" Dawson cut in. "But don't you catch on, pal? If the number is forty-five, it means that the lad is a phoney. And that means that maybe we'll get some excitement out of this aerial messenger boy job.""Rot, and very much so!" Freddy snapped angrily. "Come off it, Dave! This is very serious business, and you are absolutely balmy to even hope that things will go wrong. Just remember what Colonel Welsh said, Dave. If one of these sealed envelopes should fall into Axis hands, he'd rather put a bullet in his brain than go on living. Stop being a blasted fool, old thing! It's not a bit like you at all!"

"Okay, okay, papa!" Dawson chuckled. "Consider that you have up-ended me and given me the shingle where it counts most. Just the same, I hate to think of going stark, raving mad in the cockpit of a Wright-powered Vultee."

"Well, if that's all that's bothering you, you can put it out of your mind at once," Freddy snapped, "because you were that way a long, long time ago!"

"Oh, yeah?" Dawson shouted.

"Yeah!" Freddy Farmer replied. "But definitely!"

They left it that way for the next fifteen minutes or so. At the end of that time the Vultee was well out of sight of all land, and Dawson was keeping it on course with instruments. At the end of that time, too, the southern part of the heavens began to mist and fog up and gradually change to a copperish gray. The straight line that marked where the blue of the sky ended and the copperish gray began told Dawson that a line squall was moving across the Caribbean. But five minutes later the little twinge of uneasiness that had come to him melted away, because the copperish gray moved westward and not up northward toward the Vultee. However, because of the silly mood that had gripped him since leaving Puerto Rico, he had to voice a crazy thought.

"Wouldn't you know, not even a storm to give us something extra to do!"

"Eh, Dave?" he heard Freddy Farmer say. Then a second later, he felt Farmer's hand tapping him on the shoulder, and heard his pal's excited voice crackling in his inter-com phones. "Bear ten degrees eastward, Dave! There's something down there on the water. Can't see it clearly yet. Looks like a bit of rag being waved about by somebody."

Dawson changed the Vultee's course, and at the same time twisted around in the seat and glanced back at Freddy. Then he turned front and peered ahead and down in the direction of the English youth's pointed finger. He squinted his eyes slightly and even shielded them against the golden sun with his free hand. But for all he could see, he might just as well have kept both eyes shut. There was just blue Caribbean, turned golden here and there by shafts of sunlight dancing off the surfaces of the rolling swells.

"I know you can see through a brick wall, Freddy," he said, "but if you can see anything down there, then I'll eat it!"

"It will be quite a meal!" Freddy Farmer cried. "Because it happens to be a life raft! And there are chaps on it. Yes, four chaps! And one is waving his shirt, or something. Blast those dirty U-boat blighters!"

"Never mind the U-boats!" Dawson growled. "Just stick to the raft. Where the heck is it? I think you're seeing things. I—Hold it, everybody; hold it! I see it now, Freddy! I wasn't looking far enough out. Yeah! That's a raft sure enough. Boy! I bet this sun is doing plenty to those birds!"

As Dawson spoke, he watched the small raft riding the rolling swells of the blue Caribbean, as helpless as a leaf. As he stared at the four figures in the raft, his anger boiled and the blood throbbed in his temples. Dirty U-boat blighters, and how, as Freddy had said. Of all the fighting forces to come out of Nazi Germany, the U-boat commanders and crews were the worst. Human life, and particularly the lives of women and children, meant even less to them than it did to the Gestapo. Steel sharks of the sea, they were called. To call them that was an insult to a real man-eating shark. There just wasn't any name to call those who manned Nazi U-boats, because there is no name in any language that adequately describes them.

Yes, the dirty U-boat blighters! Down there on the bobbing raft were four who were no doubt victims of a terrible life-and-ship-destroying explosion that had probably come in the dark of night. As those and other bitter thoughts raced through Dawson's mind, he impulsively eased back the Wright-Cyclone's throttle and slanted the nose of the Vultee downward.

"How I wish this was a flying boat, and we could pick up those poor beggars!" he heard Freddy Farmer groan.

"You and me both!" Dave agreed. "We have a radio, thank goodness. So we can get help sent out before those fellows have to spend another night at sea. I wonder how long they've been floating around?"

"Quite some time, I fancy," Freddy Farmer said. "The chap waving his shirt seems to be the only one with any life in him. The three huddled down in the raft might as well be dead. Sights like that one make me thank my lucky stars I'm in the air end of this blasted war."

"You can say that again for me!" Dawson echoed. "At least in the air you get it clean and fast. Mostly, anyway. Check and double-check! The boys that really deserve the medals and the praise in this scrap are the merchant marine fellows. They have nothing to fight back with except a pea-shooter at the stern, and maybe one on the bow. They're perfect floating targets twenty-four hours a day. If their engines break down, heaven help them! Yes, my hat is off to those fellows, and I don't mean maybe. I—Hey, Freddy! See that? He's trying to send us a message with his shirt, isn't he? He seems to be waving it down to the right more than down to the left."

"That's right!" Freddy Farmer cried. "That's the old International Morse code done with a flag. To the right is a dot, and to the left is a dash. And straight down in front means the end of a word. Now, where's my blasted pencil, and I'll put it down. There he put it down in front three times! That means the end of the message. If he'll only repeat it, I think I can get it."

The man standing on the tiny raft seemed to wait a moment or two, as though he were striving to rally his waning strength for another effort. Then he started waving his shirt again. It was a short message, and both boys got it without bothering to jot down each letter. The message signaled was:

FLY OVER LOW PLEASE, IMPORTANT

"What do you make of that, Freddy?" Dawson asked, and dipped the Vultee's nose even more. "Does he think we're a rescue plane that's come to drop food and water, poor devil?"

"I don't know," the English youth replied. "Possibly. Or maybe there's something on the raft he wants us to see. The only thing to do is to go down and find out. I say! I've just remembered! I have some chocolate, Dave. I'll tie it up in my handkerchief and try to drop it right onto the raft, if you get us down low enough. But, for heaven's sake, don't hit the raft, or the water!"

"Aw gee!" Dawson grated at him. "And that's just what I was planning to do, too! You spoil all my fun, you dope! Act your age, will you?"

"Just don't take us down too low," Freddy Farmer reminded him evenly.

Dawson opened his mouth to make a fitting retort. Instead he shrugged, let Freddy's remark slide, and concentrated on getting the Vultee down as low as he possibly could. When he had reached an altitude of some ten or fifteen feet, he throttled the Wright Cyclone until it was just a shade on the good side of stalling. He guided it toward the tiny life raft. The shirt-waver had ceased his signaling and was crouching down on the raft as though he were afraid Dawson was going to bounce the Vultee's belly off the top of his hatless head.

"So you're also silly enough to think I'll come too close?" Dawson growled, as he experienced a moment of annoyance. "Well, relax, fellow! Just relax, and let's have a look at the meaning of that message. Okay, Freddy! Get set to drop that chocolate!"

As he spoke, he impulsively started to jerk his head around. Some inner warning cut short his effort, and it was that inner warning that unquestionably saved his life, and Freddy Farmer's life, too. In other words, just as he was about to turn his head for a look at Young Farmer, all four men on the raft sprang to crouching positions. Each gripped a sub-machine gun in his hands and blazed away at the coasting Vultee!

True, Dawson's sudden inner warning had helped, but it was his instinctive reaction to sudden danger that actually saved his life and Freddy's. In less time than it takes to bat an eyelash, he had smashed the throttle wide open with one hand and was hauling the Vultee around in a wing tip water-kissing turn with the other. Had he started to climb at that same time, the Grim Reaper still might have claimed them both, because the four crouching figures on the raft had automatically pointed their machine guns skyward.

As it happened, though, Dawson held the Vultee in a tight turn until its tail was toward the raft. Then he quickly flattened out, shot forward for a split second, and banked the Vultee over on its left wing tip. He banked it to the right wing tip and hauled the craft up in a twisting power zoom toward the sun-filled heavens. Only when he was well out of range and had leveled off did he let the clamped air out of his lungs and shake the cold beads of sweat from his forehead."Suffering rattlesnakes, Freddy!" he choked out. "Was that a nightmare, or did it happen? Those bums let fly at us, Freddy! All four of them!"

There was no answer from young Farmer, and in the length of time it took Dawson to twist around in the seat, he seemed to die a thousand deaths. His fears were unfounded, however. Freddy Farmer was very much alive. No bullet had snuffed out his life, though the left side of his glass hatch was covered with a million tiny cracks. Amazement and utter bewilderment were all that was wrong with the British-born air ace. He sat rigid in his seat, staring at Dawson as though he had never seen him before in his life. His face was white under his sun-and-wind bronze, and his mouth hung open as though he had intended to yell, but had been shocked into forgetting all about it.

"Hey, Freddy, snap out of it!" Dawson shouted, and rocked the Vultee violently.

The English youth stared blankly for a second longer. Suddenly he blinked, and his whole body shook like a leaf. The breath came from between his lips in a whistle that Dawson could almost hear above the roar of the Vultee's Cyclone."The blighters! The low-down dirty beggars! They shot at us; They—they—" Young Farmer choked on his words, and his eyes opened still wider in amazement.

It took a half second or so for Dawson to realize that Freddy was looking at something forward and downward. Automatically, he twisted around front and looked down. He let out a bellow of surprise. Down on the Caribbean was a Nazi U-boat breaking surface not over fifty yards from the floating life raft. Unable to move a muscle, he stared as the conning-tower hatch opened and a couple of men spilled out onto the wet deck and hurried toward the bow. The undersea killer veered over toward the floating raft.

What he saw made Dave fighting mad. He shook with anger, and a red film seemed to slide over his eyes.

"So?" he bellowed at the top of his lungs. "So it's like that, huh?"

It was just like that. No sooner had the words left Dawson's lips than the U-boat's bow gun belched flame, and the sky a hundred yards or so off the Vultee's right wing tip seemed to explode in a roar of sound and a great puff of oily black smoke. An instant later, another bit of sky seemed to explode. This time the puff of oily black smoke was high above the Vultee. This was because Dawson had turned the nose of the plane downward and was thundering straight at the U-boat at almost rocket speed.

"So you want to play, do you?" He shouted the crazy words. "Well, so do we! And how! Here, catch, you tramps!"

The Vultee's wing guns punctuated his words with a chattering blast of sound that made the aircraft tremble violently. Straight lines of silver tracers cut down at the two men crouched behind the guard of the U-boat's bow gun. They would have done better had they dived overboard and down under the U-boat's keel. The bullets from the Vultee's wing guns found them and smashed them to the steel deck. Tapping rudder a bit, Dawson veered the plane's nose a shade to the right and blazed away at the open conning tower hatch. A man crawling up out of it was flung head over heels clear of the U-boat's side and down into the water as though by some invisible giant.

By then the Vultee's prop was about ready to chew into the conning tower itself, and Dawson had to haul the nose up and go curving around and away. That maneuver permitted Freddy Farmer to go into action with his rear guns. As Dave jerked his head around for a split second, he saw the four men on the raft trying to scramble up to the U-boat's wet deck, only to go toppling over backwards like tenpins and disappear beneath the surface of the water.

"There, you rotten beggars, you'll not do that again!" the English youth's voice rang loud in Dawson's inter-com phones. "Not by half, you won't!"

"The sub's crash diving, Freddy!" Dawson yelled as he saw the hatch close and the nose of the U-boat slip down under water. "Oh, gosh! If we only had a depth charge or two! Oh, how I hate to let that snake get away!"

As the wishful words spilled off his lips, he was in the act of doing what little he could. That was wheeling around and down for another run over the crash-diving U-boat, and letting fly with all his guns at the top half of the submerging craft. He might possibly hit some part that would check the dive and force the U-boat back to the surface. That was a slim, slim hope, and it died completely as the entire craft slid out of sight, leaving behind an empty life raft and seven bodies.

With a groan Dave cut his fire, and hauled the Vultee up out of its dive and onto even keel. He stared down at the floating bodies, gulped, shuddered slightly, and drew a hand across his goggles, as though that would wipe away the scene below and make everything as it had been before. It didn't, of course, but when he took another look downward he found it hard to believe that Death had been whispering so close. Then he snapped out of his trance.

"Get the nearest patrol base on the radio, Freddy, and report that U-boat's position!" he spoke into his inter-com mike. "There's just a chance that it may have to surface soon, and somebody else can nail it."

"Right-o!" Freddy Farmer called back. "But, gosh, I would love to be that somebody else! Or—or has this just been a crazy dream, Dave? It doesn't make sense! Those were blasted Nazis on the life raft. Like—like a confounded decoy, or something. I—"

"Decoy?" Dave Dawson gasped, and sat up straight in the pit. "Holy smoke! Do you suppose so? Sure, you must be right. Look, Freddy! Report that U-boat's last position. Then we'll get out of here, but fast! Something is kind of screwy, and I don't like it, but plenty I don't."

As Dawson nosed the Vultee around and onto its course for San Fernando on British-owned Trinidad, he impulsively lifted his free hand to his chest and pressed it against the two sealed envelopes and the little vial of acid that were in his inside tunic pocket.