ten o'clock at night
Finally , if he did not throw the substance into the fire at the moment of leaving the room , who did do so ? The affair happened immediately after his departure . Had anyone else come in , the family would certainly have risen from the table . Besides , in peaceful Cornwall , visitors did not arrive after ten o'clock at night . We may take it , then , that all the evidence points to Mortimer Tregennis as the culprit . '' `` Then his own death was suicide ! '' `` Well , Watson , it is on the face of it a not impossible supposition .