“Oh! it wasn’t that I doubted your word at all, Percy; don’t think that,” Chief Waller hastened to say; for like most men he was ready to bow down in front of the golden calf; and more than once Mrs. Carberry had been very generous to the force—­when her house took fire and came near burning, but was saved, thanks to the energetic work of police and fire departments; and again, when a hired man tried to carry off some of her jewelry, but had been easily caught, and the plunder restored.

“Then what makes you act like that, I’d like to know?” demanded Percy, looking very much put out, as though he did not like to be treated with suspicion, especially when his old-time rivals, the Bird boys, were around.

“Why,” the officer went on to say, “when you said that about your aeroplane being taken, it struck me all in a heap; because Frank here was just telling me that two men broke into his shop last night after eleven, and knocked things around, just because they failed to find his hydroplane in its bunk as usual.  They wanted that machine, and wanted it so bad, that, as a last resort, they went over to your place, and confiscated your biplane.”

It was Percy’s turn now to look astonished.  He even condescended to notice the presence of the two Bird boys, and surveyed them with interest.

“Is that a fact, Frank?  Did somebody break into your place last night?  I remember now that I did see you pottering about your craft up there somewhere about the Quackenboss place, but I’d forgotten it till the Chief mentioned that you didn’t have it in the hangar.  That’s the time you were lucky.  See what I got for having mine at home all snug and nice.  It’s been hooked clear as anything, and not a trace to tell who did the business.”

“Hold on there, Percy,” said the Chief, with a broad smile, “perhaps it isn’t such a deep mystery after all.”

“Tell me what you mean when you say that,” demanded the boy, loftily, as though he resented the fact that anything should be kept from him a single second.

“Why, Frank and Andy found these things in their shop, left by the two men who tried to get their hydroplane; and the chances are ten to one the same parties went right straight over to your place and got yours as a second choice.”

“I don’t like the way you speak of my biplane, Chief, which cost ever so much more money than the contraption the Bird boys own,” Percy remarked, sneeringly; “but never mind, tell me what these things stand for.  An electric torch and—­why those things look like black masks.  Great Caesar! and the Bloomsbury bank was robbed last night, they told me when I was rushing around looking for you.  See here, do you think the yeggs who did that neat job got away with my biplane?”

Percy was getting more excited than ever now.  When he did, he seemed to just foam a little at the corners of his mouth, his eyes glittered, and his face turned red.