Now, if it had been lost and recovered, Mrs. Inglethorp would at once have replaced it on her bunch; but on her bunch I found what was obviously the duplicate key, very new and bright, which led me to the hypothesis that somebody else had inserted the original key in the lock of the despatch-case."
Since she had to put a new key on her bunch, it was obvious that someone had stolen the old one.
mnli hypothesis: Since she had to put a new key on her bunch, it was obvious that someone had stolen the old one. premise: Now, if it had been lost and recovered, Mrs. Inglethorp would at once have replaced it on her bunch; but on her bunch I found what was obviously the duplicate key, very new and bright, which led me to the hypothesis that somebody else had inserted the original key in the lock of the despatch-case."