nine o'clock
Betty had just asked for an envelope and Katherine was numbering her pages when Mary Brooks knocked at the door . `` What on earth are you girls doing ? '' she inquired blandly , selecting the biggest apple in the dish and appropriating the Morris chair , which Katherine had temporarily vacated . `` I have n't heard a sound in here since nine o'clock . I began to think that Helen had come in and blown out the gas again by mistake and you were all asphyxiated . '' Everybody laughed at the remembrance of a recent occasion when Helen had absent-mindedly blown out the gas while Betty was saying her prayers . `` It was n't so funny at the time , '' said Betty ruefully .