瓦倫丁（鎮定而謙恭地注視著神父）已經恢複了常態，“哦，”他立刻說，“個人的意見可以先保留，各位紳士務必信守承諾，不要擅自離開，並且互相監督。各位想要了解更多其他情況，可以向伊萬詢問，我必須公事公辦，並向局裏打報告。我們不能再隱瞞下去了。我一會兒會去書房寫報告，有任何新的情況，請速來找我。”
“還有其他新的情況嗎，伊萬？”瓦倫丁局長剛邁著大步出去，西蒙醫生就過來問道。
“我想，是有一件事，先生，”伊萬皺著他那張灰色的臉說，“不過從某方麵來說確實很重要。關於那個你在草坪上找到的老家夥，”他毫不客氣地指著那個臉色發黃的黑色屍體說，“不管怎麽說，有人告訴了我們他是誰。”
“真的？”西蒙醫生驚訝地喊道，“那他是誰呢？”
“他的名字叫阿諾德·貝克爾，”伊萬說，“不過，他還有許多化名。他是那種到處亂竄的流氓，據我們所知，他在美國待過，就是在那裏和布雷恩結仇的。我們沒怎麽和他打過交道，因為大部分時間他都是在德國活動。我們倒是和德國警察局進行了溝通。但是很奇怪，他還有一個雙胞胎兄弟，名叫路易斯·貝克爾，我們倒是和他經常打交道。事實上，就在昨天，他被執行死刑了。哦，這真是一個離奇的案件。先生們，當我看到這家夥躺在草坪上的時候，從未如此驚訝過。要不是我們曾親眼見到路易斯·貝克爾被執以死刑，我發誓，這個躺在草坪上的人就是他。緩過神來，我才記起他有個雙胞胎兄弟在德國，於是就按這條線索追蹤下去……”
伊萬不再解釋了，因為這會兒沒人聽他的了。奧布瑞恩長官和西蒙醫生都盯著布朗神父，布朗神父僵硬地跳起來，死死地按著太陽穴，就像一個突然劇烈頭痛的人。
“停！停！停！”他喊道，“別再說了，我已經明白了一大半。上帝，請賜予我力量吧！讓我的腦袋足夠聰明，揭開所有的謎團！上帝，快來幫幫我！我向來善於思考，我曾經闡釋過《阿奎那寶典》的每一頁。快讓我的腦袋一分為二——或者找出答案！現在，我才弄清楚一半——僅僅一半！”
他把頭埋在手中，站在那裏，就像一個正在經曆痛苦和折磨的思考者或者禱告者，而其他三個人對於這混亂的十二個小時內所發生的奇事，隻能繼續觀望。
布朗神父把手拿下來時，看起來一臉嚴肅，但是精神飽滿，像個孩子。他重重地歎了口氣，說道：“我們盡快處理這件事吧。聽我說，這是讓眾人信服的最佳辦法。”他對西蒙說，“西蒙醫生，你思維敏捷，我聽說你早上推斷出五大疑點。那麽，如果你想要弄清楚的話，就讓我來回答。”
西蒙滿腹狐疑，就連眼鏡從鼻梁上滑了下來，他都沒有發現，他立刻回答道：“好吧，疑點一：為什麽用匕首就可以殺人，卻要用笨重的軍刀？”
“因為用匕首砍不下來腦袋，”布朗冷靜地說，“對這樁案件而言，砍下腦袋是絕對有必要的。”
“為什麽？”奧布瑞恩饒有興趣地問道。
“下一個疑點？”布朗神父問道。
“為什麽死者沒有叫喊或是發出聲音？”西蒙醫生又問，“在花園裏出現軍刀確實不同尋常。”
“樹枝，”神父沮喪地說著，轉向窗戶，看著案發現場，“沒有人注意到樹枝這個關鍵細節。為什麽它們會出現在離樹木很遠的草坪上？它們不是被折斷的，而是被砍掉的。凶手當時正用軍刀耍著把戲，以此來吸引死者的注意力，讓他看如何在半空中砍斷樹枝，或者諸如此類的把戲。接著，當死者低頭看被砍下的樹枝時，軍刀不動聲色地砍來，然後人頭落地。”
“哦，”西蒙醫生慢吞吞地說，“這聽起來似乎合情合理。但是接下來的兩個疑點，你又將作何解釋？”
神父依然站在那裏，一臉嚴肅地盯著窗外，停頓了一下，接著說：
“這個花園被嚴密地包圍起來，猶如一個密不透風的房間，既然如此，那麽這個陌生男子又是如何進到花園裏來的？”
小個子神父沒有轉身，回答道：“花園裏從來沒有出現過任何陌生人。”
又是一陣沉寂。突然，一陣孩子般咯咯的笑聲打破了這種緊張的氣氛。布朗神父的這番荒謬的解釋引起了伊萬的公然嘲笑。
“噢！”伊萬喊道，“那麽，難道我們昨晚沒有把一個笨重的屍體拖到沙發上？他從來就沒有走進花園？”
“走進花園？”布朗若有所思地重複道，“不，不完全是。”
“真該死，”西蒙喊道，“一個人進了花園或者沒有進來。”
“不一定非得如此，”神父微微一笑，說道，“下個疑問是什麽，醫生？”
“我想你病得不輕，”西蒙醫生尖銳地喊道，“你要是願意回答的話，我的下一個疑問是，布雷恩是如何走出花園的？”
“他沒有走出花園。”神父說，他依然望著窗外。
“難道他沒有離開過花園？”西蒙突然喊道。
“不完全是這樣。”布朗神父說。
西蒙揮舞著拳頭，表現出典型的法國式狂躁。“一個人離開了花園，或者沒離開過。”他喊道。
“也不完全是這樣。”布朗神父說。
西蒙醫生不耐煩地猛地站起來。“我不會把多餘的時間浪費在這毫無意義的談話上，”他怒氣衝衝地喊道，“如果你不知道這個人到底是在牆裏還是牆外，那麽我不會再煩你。”
“醫生，”神父彬彬有禮地說，“我們一直相處得不錯，看在老朋友的分上，趕快告訴我你的第五個疑問。”
西蒙不耐煩地坐到門邊的椅子上，輕描淡寫地說道：“腦袋和肩膀的分離方式非常蹊蹺，好像是死者死後才被砍掉的。”
“是的，”神父一動不動地說，“這樣做隻是為了讓你更相信自己做出的錯誤假設是對的，讓你認為這顆腦袋屬於這個屍體。”
人的大腦無邊無際，那裏可以製造一切罪惡，它們在奧布瑞恩的腦袋裏迅速滋生。他仿佛看到了很多善男信女混雜在一起，在那裏，男人有了不尋常的生育能力。一個神父用蒼老的聲音說道：“離開這個可怕的花園，那裏結著雙麵果。趕快逃離這個邪惡的花園，那裏有一個死人的兩顆腦袋。”然而，當這個罪惡的念頭閃過他那古老的愛爾蘭靈魂時，法國式的智慧最終還是占了上風，於是他和其他人一樣滿腹狐疑地聽著這個古怪神父的言論。
布朗神父最後轉了過來，倚窗而立，臉埋在陰影裏。盡管如此，大家還是可以看出來，他的臉如死灰一樣蒼白，但是他說話時還是那麽有條不紊。
“各位紳士，”布朗說，“你們在花園裏找到的陌生屍體並不是貝克爾，花園裏也沒有任何陌生人的屍體。這隻是西蒙醫生的推理，我可以確定，你們看到的隻是貝克爾身體的一部分。看這裏！”（他指著那個神秘屍體的黑色身軀）“你們有生以來確實沒有見過那個人，你們曾經見過這個人嗎？”
他迅速地把那個陌生的黃色禿頭踢開，然後把旁邊那個白頭發的腦袋安了上去，完全吻合。毫無疑問，躺著的這個人就是朱利葉斯·布雷恩。
“凶手，”布朗繼續平靜地說道，“把仇人的頭砍下，然後把軍刀扔到牆外。但他是個聰明人，不隻把軍刀扔了出去，也把那顆腦袋扔了出去。隨後，他又把另外一顆腦袋匆匆安上，這樣（由於他堅持私下調查），你們就把他完全想象成了另外一個人。”
“安上另外一顆腦袋？”奧布瑞恩目不轉睛地問，“什麽另外一顆腦袋？草地上並不會長腦袋，不是嗎？”
“當然不會了，”布朗神父看著他的靴子，聲音嘶啞地說，“隻有一個地方會長。它就是斷頭台上的籃子，而它旁邊就是警察局局長瓦倫丁，在謀殺前不到一小時的時間裏，他就守候在那裏。哦，我的朋友，在把我撕成碎片之前，再聽我說一分鍾。他是個誠實的人，可是由於某種合理的原因，他變得如此瘋狂。但是，難道你們沒有從他那冷酷、灰色的眼睛裏看到一絲瘋狂嗎？他能幹出任何事，真的是任何事，隻要是與粉碎他所謂的‘十字架迷信’有關，他就會為之戰鬥終身。如今，他已經為此去殺人。布雷恩的萬貫財產會因此分散到眾多教派，如此一來，原有的格局就不會發生太大的變化，平衡也不會被打破。但是，瓦倫丁聽說布雷恩對宗教持懷疑態度，並且更傾向於支持我們。如此一來，事情就不同了。布雷恩就會資助窮困而好鬥的法國教會，以及包括《斷頭台》在內的六家民族主義報紙。此時箭已在弦上，這個狂熱者不得不鋌而走險。於是，瓦倫丁決定幹掉這個千萬富翁，他真這樣幹了，正如人們所看到的，這麽一個大偵探也能犯一次罪。他利用犯罪學，合理地降罪於貝克爾，並砍下了他的腦袋，之後放在他的公文箱中帶回了家。直到最後，他還在和布雷恩辯論，而加洛韋勳爵並沒有聽完他們的談話就離開了。隨後，瓦倫丁就把布雷恩領到這個密不透風的花園，討論刀法，並用樹枝和軍刀來示範，然後……”
麵帶傷疤的伊萬跳起來喊道：“你這個瘋子！你應該馬上去見我的主人，不然我就……”
“怎麽了？我正要過去呢，”布朗鄭重其事地說，“我必須讓他去坦白交代所有一切。”
人們都跟在一臉嚴肅的布朗身後，就像挾著一個人質或是祭品。大家湧到瓦倫丁的書房時，突然停了下來。
大偵探瓦倫丁坐在桌邊，他顯然太專注了，以至於沒有聽到門口的動靜。大家停了一會兒，西蒙醫生發現在瓦倫丁筆直優雅的後背上有什麽東西，便猛地跑過去碰了他一下。人們看見在瓦倫丁的胳膊肘邊有一個小藥盒子，瓦倫丁死在了椅子上，而他那毫無表情的臉上還帶著比加圖還自豪的神情。
Aristide Valentin， Chief of the Paris Police， was late for his dinner， and some of his guests began to arrive before him. These were， however， reassured by his confidential servant， Ivan， the old man with a scar， and a face almost as grey as his moustaches， who always sat at a table in the entrance hall-a hall hung with weapons.Valentin's house was perhaps as peculiar and celebrated as its master.It was an old house， with high walls and tall poplars almost overhanging the Seine；but the oddity-and perhaps the police value of its architecture was this：that there was no ultimate exit at all except through this front door， which was guarded by Ivan and the armoury.The garden was large and elaborate， and there were many exits from the house into the garden.But there was no exit from the garden into the world outside；all round it ran a tall， smooth， unscalable wall with special spikes at the top；no bad garden， perhaps， for a man to reflect in whom some hundred criminals had sworn to kill.
As Ivan explained to the guests， their host had telephoned that he was detained for ten minutes. He was， in truth， making some last arrangements about executions and such ugly things；and though these duties were rootedly repulsive to him， he always performed them with precision.Ruthless in the pursuit of criminals， he was very mild about their punishment.Since he had been supreme over French-and largely over European-policial methods， his great influence had been honourably used for the mitigation of sentences and the purification of prisons.He was one of the great humanitarian French freethinkers；and the only thing wrong with them is that they make mercy even colder than justice.
When Valentin arrived he was already dressed in black clothes and the red rosette-an elegant figure， his dark beard already streaked with grey. He went straight through his house to his study， which opened on the grounds behind.The garden door of it was open， and after he had carefully locked his box in its official place， he stood for a few seconds at the open door looking out upon the garden.A sharp moon was fighting with the flying rags and tatters of a storm， and Valentin regarded it with a wistfulness unusual in such scientific natures as his.Perhaps such scientific natures have some psychic prevision of the most tremendous problem of their lives.From any such occult mood， at least， he quickly recovered， for he knew he was late， and that his guests had already begun to arrive.
A glance at his drawing-room when he entered it was enough to make certain that his principal guest was not there， at any rate. He saw all the other pillars of the little party；he saw Lord Galloway， the English Ambassador-a choleric old man with a russet face like an apple， wearing the blue ribbon of the Garter.He saw Lady Galloway， slim and threadlike， with silver hair and a face sensitive and superior.He saw her daughter， Lady Margaret Graham， a pale and pretty girl with an elfish face and copper-coloured hair.He saw the Duchess of Mont St.Michel， black-eyed and opulent， and with her her two daughters， black-eyed and opulent also.He saw Dr Simon， a typical French scientist， with glasses， a pointed brown beard， and a forehead barred with those parallel wrinkles which are the penalty of superciliousness， since they come through constantly elevating the eyebrows.He saw Father Brown， of Cobhole， in Essex， whom he had recently met in England.
He saw-perhaps with more interest than any of these-a tall man in uniform， who had bowed to the Galloways without receiving any very hearty acknowledgment， and who now advanced alone to pay his respects to his host. This was Commandant O'Brien， of the French Foreign Legion.He was a slim yet somewhat swaggering figure， clean-shaven， dark-haired， and blue-eyed， and， as seemed natural in an officer of that famous regiment of victorious failures and successful suicides， he had an air at once dashing and melancholy.He was by birth an Irish gentleman， and in boyhood had known the Galloways-especially Margaret Graham.He had left his country after some crash of debts， and now expressed his complete freedom from British etiquette by swinging about in uniform， sabre and spurs.When he bowed to the Ambassador's family， Lord and Lady Galloway bent stiffly， and Lady Margaret looked away.
But for whatever old causes such people might be interested in each other， their distinguished host was not specially interested in them. No one of them at least was in his eyes the guest of the evening.Valentin was expecting， for special reasons， a man of world-wide fame， whose friendship he had secured during some of his great detective tours and triumphs in the United States.He was expecting Julius K.Brayne， that multi-millionaire whose colossal and even crushing endowments of small religions have occasioned so much easy support and easier solemnity for the American and English papers.Nobody could quite make out whether Mr Brayne was an atheist or a Mormon or a Christian Scientist；but he was ready to pour money into any intellectual vessel， so long as it was an untried vessel.One of his hobbies was to wait for the American Shakespeare-a hobby more patient than angling.He admired Walt Whitman， but thought that Luke P.Tanner， of Paris， Pa.，was more"progressive"than Whitman any day.He liked anything that he thought"progressive."He thought Valentin"progressive"，thereby doing him a grave injustice.
The solid appearance of Julius K. Brayne in the room was as decisive as a dinner bell.He had this great quality， which very few of us can claim， that his presence was as big as his absence.
He was a huge fellow， as fat as he was tall， clad in complete evening black， without so much relief as a watch-chain or a ring. His hair was white and well brushed back like a German's；his face was red， fierce and cherubic， with one dark tuft under the lower lip that threw up that otherwise infantile visage with an effect theatrical and even Mephistophelean.Not long， however， did that salon merely stare at the celebrated American；his lateness had already become a domestic problem， and he was sent with all speed into the dining-room with Lady Galloway on his arm.
Except on one point the Galloways were genial and casual enough. So long as Lady Margaret did not take the arm of that adventurer O'Brien， her father was quite satisfied；and she had not done so， she had decorously gone in with Dr Simon.Nevertheless， old Lord Galloway was restless and almost rude.
He was diplomatic enough during dinner， but when， over the cigars， three of the younger men-Simon the doctor， Brown the priest and the detrimental O'Brien(the exile in a foreign uniform)-all melted away to mix with the ladies or smoke in the conservatory， then the English diplomatist grew very undiplomatic indeed. He was stung every sixty seconds with the thought that the scamp O'Brien might be signalling to Margaret somehow；he did not attempt to imagine how.He was left over the coffee with Brayne， the hoary Yankee who believed in all religions， and Valentin， the grizzled Frenchman who believed in none.They could argue with each other， but neither could appeal to him.After a time this"progressive"logomachy had reached a crisis of tedium；Lord Galloway got up also and sought the drawing-room.He lost his way in long passages for some six or eight minutes， till he heard the high-pitched， didactic voice of the doctor， and then the dull voice of the priest， followed by general laughter.They also， he thought with a curse， were probably arguing about"science and religion".But the instant he opened the salon door he saw only one thing-he saw what was not there.He saw that Commandant O'Brien was absent， and that Lady Margaret was absent， too.
Rising impatiently from the drawing-room， as he had from the dining-room， he stamped along the passage once more. His notion of protecting his daughter from the Irish-Algerianer-do-weel had become something central and even mad in his mind.As he went towards the back of the house， where was Valentin's study， he was surprised to meet his daughter， who swept past with a white， scornful face， which was a second enigma.If she had been with O'Brien， where was O'Brien！If she had not been with O'Brien， where had she been？With a sort of senile and passionate suspicion he groped his way to the dark back parts of the mansion， and eventually found a servants'entrance that opened on to the garden.The moon with her scimitar had now ripped up and rolled away all the storm-wrack.The argent light lit up all four corners of the garden.A tall figure in blue was striding across the lawn towards the study door；a glint of moonlit silver on his facings picked him out as Commandant O'Brien.
He vanished through the French windows into the house， leaving Lord Galloway in an indescribable temper， at once virulent and vague. The blue-and-silver garden， like a scene in a theatre， seemed to taunt him with all that tyrannic tenderness against which his worldly authority was at war.The length and grace of the Irishman's stride enraged him as if he were a rival instead of a father；the moonlight maddened him.He was trapped as if by magic into a garden of troubadours， a Watteau fairyland；and， willing to shake off such amorous imbecilities by speech， he stepped briskly after his enemy.As he did so he tripped over some tree or stone in the grass；looked down at it first with irritation and then a second time with curiosity.The next instant the moon and the tall poplars looked at an unusual sight-an elderly English diplomatist running hard and crying or bellowing as he ran.