midnight
`` Of course , '' he reflected , `` they 'll want to make the most of the darkness , but I think what they 'll aim at chiefly is to get here unobserved . Therefore , I think they wo n't start until it 's dark , probably from three or four different bases . That means they 'll be here a little before dawn . I shall just motor my people up to Harrow and get back again by midnight . '' Thomson left the Admiralty , a little later , and took a taxi to Berkeley Square . The servant hesitated a little at his inquiry . `` Miss Geraldine is in , sir , I believe , '' he said .