'We should expect some small effort at disguise,' Dr. Urth observed. There will probably be certain letters and figures added to make the series appear more legitimate.'

He reached for a scratch pad and shoved another toward the Inspector. For minutes the two men were silent, jotting down serial numbers, experimenting with crossing out obviously unrelated figures.

At last Davenport let out a sigh that mingled satisfaction and frustration. 'I'm stuck,' he admitted. 'I think you're right; the numbers on the engine and the calculator are clearly disguised coordinates and dates.

They don't run anywhere near the normal series, and it's easy to strike out the fake figures. That gives us two, but I'll take my oath the rest of these are absolutely legitimate serial numbers. What are your findings, Doctor?'

Dr. Urth nodded. 'I agree. We now have two coordinates and we know where the third was inscribed.'

'We know, do we? And how-' The Inspector broke off and uttered a sharp exclamation. 'Of course! The number on the very ship itself, which isn't entered here-because it was on the precise spot on the hull where the meteor crashed through-I'm afraid there goes your silicony. Doctor.' Then his craggy face brightened. 'But I'm an idiot. The number's gone, but we can get it in a flash from Interplanetary' Registry.'

'I fear,' said Dr. Urth, 'that I must dispute at least the second part of your statement. Registry will have only the ship's original legitimate number, not the disguised coordinate to which the captain must have altered it.'

The exact spot on the hull,' Davenport muttered. 'And because of that chance shot the asteroid may be lost forever. What use to anybody are two coordinates without the third?'

'Well,' said Dr. Urth precisely, 'conceivably of very great use to a two-dimensional being. But creatures of our dimensions,' he patted his paunch, 'do require the third-which I fortunately happen to have right here.'

'In the T.B.I, dossier? But we just checked the list of numbers-'

'Your list, Inspector. The file also includes young Vernadsk's original report. And of course the serial number listed there for the Robert Q. is the carefully faked one under which she was then sailing-no point in rousing the curiosity of a repair mechanic by letting him note a discrepancy.'

Davenport reached for a scratch pad and the Vernadsky list. A moment's calculation and he grinned.

Dr. Urth lifted himself out of the chair with a pleased puff and trotted to the door. 'It is always pleasant to see you. Inspector Davenport. Do come again. And remember the government can have the uranium, but

I want the important thing: one giant silicony, alive and in good condition.' He was smiling. 

'And preferably,' said Davenport, 'whistling.' Which he was doing himself as he walked out.

Of course, there is a catch about writing a mystery. You are apt to concentrate so bard on the mystery itself, on occasion, as to lose sight of important peripheral values. After this story first appeared, I received quite a bit of mail expressing interest in the silicony and, in some cases, finding fault with me for allowing it to die in so coldblooded a fashion. As I reread the story now, I must admit the readers are right. I showed a lack of sensitivity to the silicony's rather pathetic death because I was concentrating on his mysterious last words. If I had to do it over again, I would certainly be warmer in my treatment of the poor thing. I apologize.

This shows that even experienced writers don't always do the Right Thing, and can miss something that is bobbing up and down right at mustache level.

This next story is not, in the strictest sense of the word, a science fiction mystery, yet I include it. The reason is that science is closely and intimately involved with the mystery, and I hesitate to penalize it by non-inclusion merely because the science is of the present rather than of the future.

If you think it's hard to get hold of potassium cyanide, think again. I stood there with a pound bottle in my hand. Brown glass, a nice clear label saying 'Potassium Cyanide CP' (the initials, I was told, meaning 'chemically pure') with a small skull and crossbones underneath.

The fellow who owned the bottle polished his glasses and blinked at me. He was Associate Professor Helmuth Rodney of Carmody University. He was of middle height, stocky, with a soft chin, plump lips, a budding paunch, a shock of brown hair, and a look of complete indifference to the fact that I was holding in my hand enough poison to kill a regiment.

I said, 'Do you mean to say this just stands on your shelf, Professor?'

He said in the kind of deliberate tone he probably used in lecturing his students, 'Yes, it always has, Inspector. Along with the rest of the chemicals in alphabetic order.'

I glanced about the cluttered room. Shelves lined the upper reaches of all the walls, and bottles, large and small, filled them all.

This one,' I pointed out, 'is poison.'

'A great many of them are,' he said with composure.

'Do you keep track of what you've got?'

'In a general way.' He rubbed his chin. 'I know I have that bottle.'

'But suppose someone came in here and helped himself to a spoonful of this stuff. Would you be able to tell?'

Professor Rodney shook his head. 'I couldn't possibly.'

'Well, then, who could get into this laboratory? It is kept locked?' 

He said, 'It's locked when I leave in the evening, unless I forget. During the day, it isn't locked, and I'm in and out.'

'In other words. Professor, anyone could come in here, even someone from the street, walk off with some of the cyanide, and no one would ever know.'

'I'm afraid so.'

'Tell me. Professor, why do you keep this much cyanide in the place anyway? To kill rats?'

'Good heavens, no.' He seemed family repelled at the thought. 'Cyanide is sometimes used in organic reactions to form necessary intermediates, to provide a proper basic medium, to catalyze-'

'I see. I see. Now in what other labs is cyanide available in this way?'

'In most of them,' he answered at once. 'Even in the student labs. After all, it's a common chemical, routinely used in syntheses.'

'I wouldn't call its use today routine,' I said.

He sighed and said, 'No, I suppose not.' He added thoughtfully, They used to call them the "Library Twins." '

I nodded. I could see the reason for the nickname. The two girl librarians were very alike.

Not close up, of course. One had a small pointed chin on a round face, and the other had a square jaw and a long nose. Still, bend them over a desk and both had honey-blond hair parted in the middle with a similar wave. Look them quickly in the face and you would probably notice first wide-set eyes of about the same shade of blue. See them standing together at a moderate distance and you could see they were both of a height and both, probably, with the same brand and size uplift brassiere. Both had trim waists and neat legs. Today they had even dressed similarly. Both wore blue.

There was no confusing the two now, though. The one with the small chin and round face was full of cyanide, and quite dead.

The similarity was the first thing that struck me when I arrived with my partner, Ed Hathaway. There was one girl slumped in her chair and dead, her eyes open, one arm dangling straight down, with a broken teacup on the floor beneath like a period under an exclamation point. Her name, it turned out, was Louella-Marie Busch. There was a second girl, like the first one brought back to life, white and shaken, staring straight ahead and letting the police and their work flow about her without seeming to notice. Her name was Susan Morey.