Betty tucked the box under her arm. No one disputed her right to carry it, for the other girls deferred to the Little Captain in matters of this sort.
"Won't the boys be surprised when they see it!" commented Amy.
"But listen!" cautioned Betty. "We mustn't pretend that we think there is anything in it. If we do, and there isn't, they'd have the laugh on us."
"Oh, of course," assented Grace. "We'll just say we found the box on the beach, and couldn't open it. The boys will be anxious enough to do that."
And, sure enough, when the girls reached the cottage, the boys being not far behind them, the latter were even more eager than Betty and her chums to have a look inside the mysterious iron case.
"Pry the cover off!" cried Will, when he and the others had briefly related their experience in saving their motor boat and sailing back in the other craft, while the girls gave their story bit by bit, from the sighting of the men in the boat, to the finding of the box. Only Betty said nothing about the faces at the window of the fisherman's hut.
"Pry the cover off!" cried Will. "An axe is the best thing to use!"
"Indeed not!" exclaimed Betty. "Let's see if we can't open it with a key. You have some odd ones; haven't you, Daddy?"
"Yes," assented Mr. Nelson, who was down at the shore for the week-end. "Betty, get them. You'll find them in that desk in the living room."
Betty's father had looked at the box on all sides, had shaken it, and had examined the lock through a reading glass.