thief　had　not　brought　a　parcel　with　him；　he　had　made　one　here　…　a
  parcel　with　the　stolen　objects；　no　doubt；　and　he　put　it　in　this
  corner　intending　to　take　it　away　when　the　moment　came　for　him　to
  make　his　escape。　　He　had　also　placed　his　heavy　boots　beside　the
  parcel；　…　for；　see　…　there　are　no　marks　of　steps　leading　to　the
  marks　left　by　the　boots；　which　were　placed　side　by　side。　　That
  accounts　for　the　fact　that　the　murderer　left　no　trace　of　his　steps
  when　he　fled　from　The　Yellow　Room；　nor　any　in　the　laboratory；　nor　in
  the　vestibule。　　After　entering　The　Yellow　Room　in　his　boots；　he　took
  them　off；　finding　them　troublesome；　or　because　he　wished　to　make　as
  little　noise　as　possible。　　The　marks　made　by　him　in　going　through
  the　vestibule　and　the　laboratory　were　subsequently　washed　out　by
  Daddy　Jacques。　　Having；　for　some　reason　or　other；　taken　off　his
  boots；　the　murderer　carried　them　in　his　hand　and　placed　them　by　the
  side　of　the　parcel　he　had　made；　…　by　that　time　the　robbery　had　been
  accomplished。　　The　man　then　returned　to　The　Yellow　Room　and　slipped
  under　the　bed；　where　the　mark　of　his　body　is　perfectly　visible　on
  the　floor　and　even　on　the　mat；　which　has　been　slightly　moved　from
  its　place　and　creased。　　Fragments　of　straw　also；　recently　torn；　bear
  witness　to　the　murderer's　movements　under　the　bed。〃
  〃Yes；　yes；　…　we　know　all　about　that；〃　said　Monsieur　de　Marquet。
  〃The　robber　had　another　motive　for　returning　to　hide　under　the　bed；〃
  continued　the　astonishing　boy…journalist。　　〃You　might　think　that　he
  was　trying　to　hide　himself　quickly　on　seeing；　through　the　vestibule
  window；　Monsieur　and　Mademoiselle　Stangerson　about　to　enter　the
  pavilion。　　It　would　have　been　much　easier　for　him　to　have　climbed
  up　to　the　attic　and　hidden　there；　waiting　for　an　opportunity　to　get
  away；　if　his　purpose　had　been　only　flight。　…　No！　　No！　…　he　had　to
  be　in　The　Yellow　Room。〃
  Here　the　Chief　intervened。
  〃That's　not　at　all　bad；　young　man。　　I　compliment　you。　　If　we　do　not
  know　yet　how　the　murderer　succeeded　in　getting　away；　we　can　at　any
  rate　see　how　he　came　in　and　committed　the　robbery。　　But　what　did　he
  steal？〃
  〃Something　very　valuable；〃　replied　the　young　reporter。
  At　that　moment　we　heard　a　cry　from　the　laboratory。　　We　rushed　in
  and　found　Monsieur　Stangerson；　his　eyes　haggard；　his　limbs
  trembling；　pointing　to　a　sort　of　bookcase　which　he　had　opened；　and
  which；　we　saw；　was　empty。　　At　the　same　instant　he　sank　into　the
  large　armchair　that　was　placed　before　the　desk　and　groaned；　the
  tears　rolling　down　his　cheeks；　〃I　have　been　robbed　again！　　For　God's
  sake；　do　not　say　a　word　of　this　to　my　daughter。　　She　would　be　more
  pained　than　I　am。〃　　He　heaved　a　deep　sigh　and　added；　in　a　tone　I
  shall　never　forget：　〃After　all；　what　does　it　matter；　…　so　long　as
  she　lives！〃
  〃She　will　live！〃　said　Monsieur　Darzac；　in　a　voice　strangely　touching。
  〃And　we　will　find　the　stolen　articles；〃　said　Monsieur　Dax。　　〃But
  what　was　in　the　cabinet？〃
  〃Twenty　years　of　my　life；〃　replied　the　illustrious　professor　sadly；
  〃or　rather　of　our　lives　…　the　lives　of　myself　and　my　daughter！　　Yes；
  our　most　precious　documents；　the　records　of　our　secret　experiments
  and　our　labours　of　twenty　years　were　in　that　cabinet。　　It　is　an
  rreparable　loss　to　us　and；　I　venture　to　say；　to　science。　　All　the
  processes　by　which　I　had　been　able　to　arrive　at　the　precious　proof
  of　the　destructibility　of　matter　were　there　…　all。　　The　man　who　came
  wished　to　take　all　from　me；　…　my　daughter　and　my　work　…　my　heart
  and　my　soul。〃
  And　the　great　scientist　wept　like　a　child。
  We　stood　around　him　in　silence；　deeply　affected　by　his　great
  distress。　　Monsieur　Darzac　pressed　closely　to　his　side；　and　tried
  in　vain　to　restrain　his　tears　…　a　sight　which；　for　the　moment；
  almost　made　me　like　him；　in　spite　of　an　instinctive　repulsion　which
  his　strange　demeanour　and　his　inexplicable　anxiety　had　inspired　me。
  Monsieur　Rouletabille　alone；　…　as　if　his　precious　time　and　mission
  on　earth　did　not　permit　him　to　dwell　in　the　contemplation　on　human
  suffering　…　had；　very　calmly；　stepped　up　to　the　empty　cabinet　and；
  pointing　at　it；　broke　the　almost　solemn　silence。　　He　entered　into
  explanations；　for　which　there　was　no　need；　as　to　why　he　had　been　led
  to　believe　that　a　robbery　had　been　committed；　which　included　the
  simultaneous　discovery　he　had　made　in　the　lavatory；　and　the　empty
  precious　cabinet　in　the　laboratory。　　The　first　thing　that　had　struck
  him；　he　said；　was　the　unusual　form　of　that　piece　of　furniture。　　It
  was　very　strongly　built　of　fire…proof　iron；　clearly　showing　that　it
  was　intended　for　the　keeping　of　most　valuable　objects。　　Then　he
  noticed　that　the　key　had　been　left　in　the　lock。　　〃One　does　not
  ordinarily　have　a　safe　and　leave　it　open！〃　he　had　said　to　himself。
  This　little　key；　with　its　brass　head　and　complicated　wards；　had
  strongly　attracted　him；　…　its　presence　had　suggested　robbery。
  Monsieur　de　Marquet　appeared　to　be　greatly　perplexed；　as　if　he　did
  not　know　whether　he　ought　to　be　glad　of　the　new　direction　given　to
  the　inquiry　by　the　young　reporter；　or　sorry　that　it　had　not　been
  done　by　himself。　　In　our　profession　and　for　the　general　welfare；　we
  have　to　put　up　with　such　mortifications　and　bury　selfish　feelings。
  That　was　why　Monsieur　de　Marquet　controlled　himself　and　joined　his
  compliments　with　those　of　Monsieur　Dax。　　As　for　Monsieur　Rouletabille；
  he　simply　shrugged　his　shoulders　and　said：　〃There's　nothing　at　all
  in　that！〃　　I　should　have　liked　to　box　his　ears；　especially　when　he
  added：　〃You　will　do　well；　Monsieur；　to　ask　Monsieur　Stangerson　who
  usually　kept　that　key？〃
  〃My　daughter；〃　replied　Monsieur　Stangerson；　〃she　was　never　without　it。
  〃Ah！　　then　that　changes　the　aspect　of　things　which　no　longer
  corresponds　with　Monsieur　Rouletabille's　ideas！〃　cried　Monsieur　de
  Marquet。　　〃If　that　key　never　left　Mademoiselle　Stangerson；　the
  murderer　must　have　waited　for　her　in　her　room　for　the　purpose　of
  stealing　it；　and　the　robbery　could　not　have　been　committed　until
  after　the　attack　had　been　made　on　her。　　But　after　the　attack　four
  persons　were　in　the　laboratory！　　I　can't　make　it　out！〃
  〃The　robbery；〃　said　the　reporter；　〃could　only　have　been　committed
  before　the　attack　upon　Mademoiselle　Stangerson　in　her　room。　　When
  the　murderer　entered　the　pavilion　he　already　possessed　the
  brass…headed　key。〃
  〃That　is　impossible；〃　said　Monsieur　Stangerson　in　a　low　voice。
  〃It　is　quite　possible；　Monsieur；　as　this　proves。〃
  And　the　young　rascal　drew　a　copy　of　the　〃Epoque〃　from　his　pocket；
  dated　the　21st　of　October　（I　recall　the　fact　that　the　crime　was
  committed　on　the　night　between　the　24th　and　25th）；　and　showing　us
  an　advertisement；　he　read：
  〃'Yesterday　a　black　satin　reticule　was　lost　in　the　Grands　Magasins
  de　la　Louvre。　　It　contained；　amongst　other　things；　a　small　key　with
  a　brass　head。　　A　handsome　reward　will　be　given　to　the　person　who
  has　found　it。　　This　person　must　write；　poste　restante；　bureau　40；　to
  this　address：　M。　A。　T。　H。　S。　N。'　　Do　not　these　letters　suggest
  Mademoiselle　Stangerson？〃　continued　the　reporter。　　〃The　'key　with
  a　brass　head'　…　is　not　this　the　key？　　I　always　read　advertisements。
  In　my　business；　as　in　yours；　Monsieur；　one　should　always　read　the
  personals。'　They　are　often　the　keys　to　intrigues；　that　are　not
  lways　brass…headed；　but　which　are　none　the　less　interesting。　　This
  dvertisement　interested　me　specially；　the　woman　of　the　key　surrounded
  it　with　a　kind　of　mystery。　　Evidently　she　valued　the　key；　since　she
  promised　a　big　reward　for　its　restoration！　　And　I　thought　on　these
  six　letters：　M。　A。　T。　H。　S。　N。　　The　first　four　at　once　pointed　to
  a　Christian　name；　evidently　I　said　Math　is　Mathilde。　　But　I　could
  make　nothing　of　the　two　last　letters。　　So　I　threw　the　journal　aside
  and　occupied　myself　with　other　matters。　　Four　days　later；　when　the
  evening　paper　appeared　with　enormous　head…lines　announcing　the　murder
  of　Mademoiselle　Stangerson；　the　letters　in　the　advertisement
  mechanically　recurred　to　me。　　I　had　forgotten　the　two　last　letters；
  S。　N。　　When　I　saw　them　again　I　could　not　help　exclaiming；
  'Stangerson！'　　I　jumped　into　a　cab　and　rushed　into　the　bureau　No。
  40；　asking：　'Have　you　a　letter　addressed　to　M。　A。　T。　H。　S。　N。？'
  The　clerk　replied　that　he　had　not。　　I　insisted；　begged　and　entreated
  him　to　search。　　He　wanted　to　know　if　I　were　playing　a　joke　on　him；
  and　then　told　me　that　he　had　had　a　letter　with　the　initials
  M。　A。　T。　H。　S。　N；　but　he　had　given　it　up　three　days　ago；　to　a　lady
  who　came　for　it。　　'You　come　to…day　to　claim　the　letter；　and　the　day
  before　yesterday　another　gentleman　claimed　it！　　I've　had　enough　of
  this；'　he　concluded　angrily。　　I　tried　to　question　him　as　to　the　two
  persons　who　had　already　claimed　the　letter；　but　whether　he　wished
  to　entrench　himself　behind　professional　secrecy；　…　he　may　have
  thought　that　he　had　already　said　too　much；　…　or　whether　he　was
  disgusted　at　the　joke　that　had　been　played　on　him　…　he　would　not
  answer　any　of　my　questions。〃
  Rouletabille　paused。　　We　all　remained　silent。　　Each　drew　his　own
  conclusions　from　the　strange　story　of　the　poste　restante　letter。
  It　seemed；　indeed；　that　we　now　had　a　thread　by　means　of　which　we
  should　be　able　to　follow　up　this　extraordinary　mystery。
  〃Then　it　is　almos