At breakfast Sir Nathaniel noticed that Adam was put out about something, but he said nothing.  The lesson of silence is better remembered in age than in youth.  When they were both in the study, where Sir Nathaniel followed him, Adam at once began to tell his companion of what had happened.  Sir Nathaniel looked graver and graver as the narration¹ proceeded, and when Adam had stopped he remained silent for several minutes, before speaking.  
“This is very grave.  I have not formed any opinion yet; but it seems to me at first impression that this is worse than anything I had expected.”
 
“Why, sir?” said Adam.  “Is the killing² of a mongoose—no matter by whom—so serious a thing as all that?”
 
His companion smoked on quietly for quite another few minutes before he spoke³.
 
“When I have properly thought it over I may moderate my opinion, but in the meantime it seems to me that there is something dreadful behind all this—something that may affect all our lives—that may mean the issue of life or death to any of us.”
 
Adam sat up quickly.
 
“Do tell me, sir, what is in your mind—if, of course, you have no objection, or do not think it better to withhold⁴ it.”
 
“I have no objection, Adam—in fact, if I had, I should have to overcome it.  I fear there can be no more reserved thoughts between us.”
 
“Indeed, sir, that sounds serious, worse than serious!”
 
“Adam, I greatly fear that the time has come for us—for you and me, at all events—to speak out plainly to one another.  Does not there seem something very mysterious about this?”
 
“I have thought so, sir, all along.  The only difficulty one has is what one is to think and where to begin.”
 
“Let us begin with what you have told me.  First take the conduct of the mongoose.  He was quiet, even friendly and affectionate with you.  He only attacked the snakes, which is, after all, his business in life.”
 
“That is so!”
 
“Then we must try to find some reason why he attacked Lady Arabella.”
 
“May it not be that a mongoose may have merely the instinct to attack, that nature does not allow or provide him with the fine reasoning powers to discriminate⁵ who he is to attack?”
 
“Of course that may be so.  But, on the other hand, should we not satisfy ourselves why he does wish to attack anything?  If for centuries, this particular animal is known to attack only one kind of other animal, are we not justified⁶ in assuming that when one of them attacks a hitherto unclassed animal, he recognises in that animal some quality which it has in common with the hereditary⁷ enemy?”
 
“That is a good argument, sir,” Adam went on, “but a dangerous one.  If we followed it out, it would lead us to believe that Lady Arabella is a snake.”
 
“We must be sure, before going to such an end, that there is no point as yet unconsidered which would account for the unknown thing which puzzles us.”
 
“In what way?”
 
“Well, suppose the instinct works on some physical basis—for instance, smell.  If there were anything in recent juxtaposition⁸ to the attacked which would carry the scent⁹, surely that would supply the missing cause.”
 
“Of course!” Adam spoke with conviction.
 
“Now, from what you tell me, the negro had just come from the direction of Diana’s Grove¹⁰, carrying the dead snakes which the mongoose had killed the previous morning.  Might not the scent have been carried that way?”
 
“Of course it might, and probably was.  I never thought of that.  Is there any possible way of guessing approximately how long a scent will remain?  You see, this is a natural scent, and may derive¹¹ from a place where it has been effective for thousands of years.  Then, does a scent of any kind carry with it any form or quality of another kind, either good or evil?  I ask you because one ancient name of the house lived in by the lady who was attacked by the mongoose was ‘The Lair¹² of the White Worm.’  If any of these things be so, our difficulties have multiplied indefinitely.  They may even change in kind.  We may get into moral entanglements¹³; before we know it, we may be in the midst of a struggle between good and evil.”
 
Sir Nathaniel smiled gravely.
 
“With regard to the first question—so far as I know, there are no fixed¹⁴ periods for which a scent may be active—I think we may take it that that period does not run into thousands of years.  As to whether any moral change accompanies a physical one, I can only say that I have met no proof of the fact.  At the same time, we must remember that ‘good’ and ‘evil’ are terms so wide as to take in the whole scheme of creation, and all that is implied by them and by their mutual¹⁵ action and reaction.  Generally, I would say that in the scheme of a First Cause anything is possible.  So long as the inherent forces or tendencies of any one thing are veiled from us we must expect mystery.”
 
“There is one other question on which I should like to ask your opinion.  Suppose that there are any permanent forces appertaining to the past, what we may call ‘survivals,’ do these belong to good as well as to evil?  For instance, if the scent of the primaeval monster can so remain in proportion to the original strength, can the same be true of things of good import?”
 
Sir Nathaniel thought for a while before he answered.
 
“We must be careful not to confuse the physical and the moral.  I can see that already you have switched on the moral entirely¹⁶, so perhaps we had better follow it up first.  On the side of the moral, we have certain justification¹⁷ for belief in the utterances¹⁸ of revealed religion.  For instance, ‘the effectual fervent¹⁹ prayer of a righteous man availeth much’ is altogether for good.  We have nothing of a similar kind on the side of evil.  But if we accept this dictum we need have no more fear of ‘mysteries’: these become thenceforth merely obstacles.”
 
Adam suddenly changed to another phase of the subject.
 
“And now, sir, may I turn for a few minutes to purely²⁰ practical things, or rather to matters of historical fact?”
 
Sir Nathaniel bowed acquiescence²¹.
 
“We have already spoken of the history, so far as it is known, of some of the places round us—‘Castra Regis,’ ‘Diana’s Grove,’ and ‘The Lair of the White Worm.’  I would like to ask if there is anything not necessarily of evil import about any of the places?”
 
“Which?” asked Sir Nathaniel shrewdly.
 
“Well, for instance, this house and Mercy Farm?”
 
“Here we turn,” said Sir Nathaniel, “to the other side, the light side of things.  Let us take Mercy Farm first.  When Augustine was sent by Pope Gregory to Christianise England, in the time of the Romans,............