eleven o'clock
ventured Andy . `` That 's what they were ; but see here , are you two just guessing this , or do you happen to know something about those men ? '' asked the other , quickly ; for he could not help seeing from the manner of the Bird boys that they were on some sort of a scent ; and he knew from past experiences that their sagacity could always be trusted to do the right thing . `` Well , '' Frank went on to say , drily , `` while Andy was watching our new hydroplane out in the Quackenboss pasture , I worked until eleven o'clock in our shop , and then went home . This morning , early , after a bite to eat , I hurried over there to do some finishing touches and carry the thing out to apply to our broken plane , when to my astonishment I found that the shop had been broken into later in the night , as well as our hangar , where the aeroplane is usually kept . And here 's what I discovered lying on the work-bench , where the men had forgotten them . '' With these words he held up the flashlight torch , and the twin black masks ; and they produced an immediate shock upon the Chief of Police .