nine o'clock
`` There is someone in my household whose suspicions you do not wish to arouse ? '' he suggested . `` There is . Shall we make it nine o'clock ? '' `` Why not come to dinner ? '' `` Thanks all the same , but I think it would serve my purpose better if I came later . '' * * * * * Dr. Cairn and his son dined alone together in Half-Moon Street that night .