flow would spark off, and we'd get a big explosion that would wreck everything—including us." Then he muttered to himself: "I still don't see how it could happen."

Jayjay Kelvin pulled a nine of spades from the back of the deck to the front. It matched the four of spades that had come three cards before. Jayjay discarded the two cards between the spades. "You don't?" he asked. "Didn't you ever hear that the total is greater than the sum of its parts?"

"What?" Captain Al-Amin sounded as though he'd been insulted—in Arabic. "What are you talking about, Mr. Kelvin?"

"I'm talking about the idiocy of the checking system," Jayjay said flatly. "Don't you see what they did? Don't you see what happened? Each part of a screamer has to be checked separately, right?"

Al-Amin nodded.

"Why? Because the things burn out if you check them as a complete unit. It's like checking a .50 caliber cartridge. The only way you can check a cartridge is to shoot it in a gun. If it works, then you know it works. Period. The only trouble is that you've wasted the cartridge. You know that that one is good, but you've ruined it.

"Same way with a screamer. If you test it as a unit, you'll ruin it. So you test it a part at a time. All the parts check out nicely because the test mechanisms are built to check each part."

Smith squinted. "Well, sure. If you check out the whole screamer, you'll ruin it. So what?"

"So suppose you were going to check out a cartridge," Jayjay said. "You don't fire it; you check each part separately. You check the brass case. It's all right; the tests show that it won't burst under firing pressure. You check the primer; the tests show that it will explode when hit by the gun's hammer. You check the powder; the tests show that the powder will burn nicely when the flame from the primer hits it. You check the bullet; the tests show that the slug will be expelled at the proper velocity when the powder is ignited.

"So you assume that the cartridge will function when fired.

"But will it?"

"Why wouldn't it?" Smith asked.

"Because the flame from the exploding primer can't reach the powder, that's why!" Jayjay snapped. "Some jerk has redesigned the primer so that the flame misses the propellant!"

"How could that happen?" Hull asked blankly.

"How? Because Designer A decided that the male plug on the screamer should have one more turn on its threads, but he forgot to tell Designer B, who designs the female plug, that the two should match. The testing equipment is designed to test each part, so each part tests out fine. The only trouble is that the thing doesn't test out as a whole."

Captain Al-Amin nodded slowly. "That's right. The test showed that the oxyhydrogen section worked fine. It showed that the starter worked fine. It showed that the radiowave broadcaster worked fine. But it didn't show that they'd work together."

Smith said a short, five-letter word. It was French; the Anglo-Saxon equivalent has only four letters. "What good does all this theorizing do us?" he added. "The question is: How do we fix the thing?"

"Well, can't you put another turn on the thread?" Hull asked.

"Oh, sure," Smith said sarcastically. "You give me a lathe and the proper tools, and I'll make you all the connections you want. Hell, if I had the proper tools, I could turn us out a new spaceship, and we could all go home in comfort."

"Couldn't you drill out the metal with that drill?" Hull asked plaintively.

"No!" Smith said harshly. "How do you expect me to get a quarter-inch bit into a space less than a sixteenth of an inch in diameter?"

Hull wasn't used to machinist's terms. "How big is an inch?"

"Two point five four oh oh oh five centimeters," Smith said in a nasty tone of voice. "Does that help you any?"

"I'm just trying to help!" Hull snapped. "You've got no call to get sarcastic with me!"

Smith said the French word again.

"Enough!" the captain barked. "Smith, control your tongue! That sort of thing won't help us." He jerked his head around. "Mr. Kelvin, do you have any suggestions?"

Jayjay played another card. "No. Not yet. I'm thinking."

"Smith? Any ideas?" The tone of the Arab's voice left no doubt that he meant business.

"No, sir. Without a properly equipped machine shop, there's nothing we can do."

"How so?"

"Because that's a precision job, sir. The threads are tapered so that the fit will be gas-tight. That's why the threads have a ten-thousandth of an inch of soft polyethylene covering the hard steel, so that when the threads are tight, the polyethylene will act as a seal. Everything in that connection is a precision fitted job. The ends of the tubes are made to be slightly mashed together, so that the seals will be tight—they're coated with polyethylene, too. If the oxygen and hydrogen mix, the efficiency of the fuel cell goes down to zero, and you run the chance of an explosion."

"Show me," Al-Amin said.

Smith took a pencil out of his pocket and began drawing a cross section of the connection on the top of the nearby table.

"Look here, captain, this is the way the two are supposed to fit. But they don't, because the male plug can't get far enough into the female socket to make the connection. Like this, see?"

The captain nodded.

"Well," Smith continued, "there's a thirty-second of an inch clearance there. If the female had one more turn of thread, the fit would be prefect. As it is, we get no connection. So the screamer doesn't function."

Al-Amin looked at the drawing. "Odd that there's never been any complaint about this error before."

Jayjay turned another ace. "Not so odd, really."

All heads turned toward Jayjay.

"What does that mean?" Smith asked.

"Just what I said." Jayjay turned another card. "A screamer is supposed to call for help, isn't it? It's only used in a dire emergency. Then the only test of the whole unit comes when the occupants of the spaceship are in danger—as we are. If the things don't work, how could there be any complaint? If we can't get ours to work, will we complain? To whom?

"How many ships have been reported missing in the past year or so? All of them presumed lost because of meteor strikes, eh? If a ship is lost and doesn't signal, we presume that it was totally destroyed. If it wasn't, they'd have signaled. As Mister Smith says: See?"

There was a long silence.

Jayjay Kelvin turned the last card, saw that he had lost, and began shuffling the deck.

"I think I've got it," Smith said excitedly, several hours later.

Captain Al-Amin glanced around. Hull was dozing fitfully a few inches above the couch. Jayjay Kelvin was still methodically playing solitaire.

"Keep your voice down," the captain ordered. "No use giving our passengers false hopes. What do you mean, you've got it?"

"Simple. Real simple. All we have to do is file off the last thread of the male plug. Then it will fit into the female." Smith's voice was a hoarse whisper.

"Won't work," said Jayjay Kelvin from across the room.

Smith blew up. "How do you know?" he roared. "You sit over there making wiseacre remarks and do nothing! Play cards, that's all! What do you know about things like this, Mister Joseph Kelvin? What does a businessman know about mechanical equipment?"

"Enough," Jayjay said quietly. "Enough to know that, if you try to file off the final thread of the male plug, you'll do an uneven job. And that will mean leakage."

"What do you mean, an uneven job?" Smith was still furious.

"Trimming off the end of the male plug would have to be done on a lathe," Jayjay said, without looking up from his cards. "Otherwise, the fit would be wrong, and the gases would mix. And we would all go phfft! when the mixture blew."

Smith started to say something, but Jayjay went right on talking. "Even if we had a lathe, the male plug doesn't