The one is whether any crime has been committed at all; the second is, what is the crime and how was it committed?
Of course, if Dr.Mortimer's surmise should be correct, and we are dealing with forces outside the ordinary laws of Nature, there is an end of our investigation.

But we are bound to exhaust all other hypotheses before falling back upon this one.

I think we'll shut that window again, if you don't mind.

It is a singular thing, but I find that a concentrated atmosphere helps a concentration of thought.

I have not pushed it to the length of getting into a box to think, but that is the logical outcome of my convictions.