six o'clock
`` That is , '' continued Hiram , `` he had n't got back when I was last up at the Aegis hangar . '' `` When was that ? '' `` About four o'clock this afternoon . Mr. Grimshaw , though , said he expected him on the six o'clock train . '' `` We 'll go and see if he has returned , '' said Dave . They started for the aviator 's headquarters . Half the distance covered , they met him coming in search of them .