five o'clock
`` Absolutely certain . '' `` Were you alone ? '' `` Yes , all alone . Sylvester left at five o'clock '' `` Who knew the combination of the safe ? '' `` Only Rochester and I. '' It was Ferguson 's turn to spring up `` By -- ! '' he exclaimed . `` I thought the electric bulbs in the office felt warm , as if they had recently been burning -- Rochester must have been there just before me . ''