nine o'clock
It seems very mysterious to me . '' `` Yes , and to every one , '' said Percival . Mr. and Mrs. Van der Donk came in shortly , and for a time there was a very pleasant conversation , but at last the old gentleman got upon the subject of his family , and before long the boys were yawning , and the old lady fast asleep . `` You will have to excuse us , '' said Percival , getting up , `` but we boys had very little sleep last night , and we have to be back at nine o'clock in any event . '' The boys took their leave , and when once clear of the house Percival said with a grin : `` I could not stand the old man and his genealogy , although we could have stayed an hour longer easily . '' `` I saw that you were beginning to yawn , and I must confess that I felt a bit drowsy myself . '' `` We wo n't find out anything about the watch through that girl , Jack , '' said Percival a little later .