"I'd like to catch 'em, myself," he said slowly in such a low voice that Sidney barely caught the words. "Oh, Lav, why not? We have as good a chance as anyone, knowing as much as we do. What'll we do first?" For Sidney was ready for adventure. Suddenly Lavender realized that he was gripping the knife in his hand. He looked down at it. "What we ought to do first is to find out how this knife got here. Let's put it where we found it and go back around the other side of that schooner so's no one on the _Puritan_'ll see us. Then we can come out late this afternoon and if it's gone--well, we'll know someone came to look for it!" "And then we'd know for sure that someone had been on the _Arabella_." "That's the idea. You get on quickly for a girl, Sid. Come on, now, we'll pull the dory round to the starboard side." Sidney caught herself tiptoeing across the deck of the_ Arabella_. In her excitement she scarcely breathed. Every move, every act, was fraught with significance. Lavender took the precaution to beach the dory at an abandoned wharf near Sunset Lane. "Just as well not to show ourselves 'round Rockman's." "When can we go out to the _Arabella_?" "Not 'till four o'clock. We can go out to swim just like we always do. Even if they see us they won't think it's funny for us to do that. They'd think it funnier if we didn't." Sidney admitted the truth of this, but wondered how she could live until four o'clock! As they walked up Sunset Lane Sidney reminded Lavender that, because of their promise, they ought to tell Mart. But when they stopped at the Calkins' house they found that Mart had already gone to Gert Bartow's. "Oh, dear," sighed Sidney, with an added pang of remorse. At four o'clock Sidney and Lavender went out to the _Arabella_ to swim as they had done always before Pola's coming. Except for a brightness in Sidney's eyes, an alertness about her whole body, and the occasional significant glances that passed between them they both appeared quite normal. Lav talked casually of the heat of the day. "Gee, the water'll feel great. This is the hottest day we've had yet." "I can't wait to get in." Most certainly Jed Starrow, had he been listening, could not have guessed how closely Nemesis pressed upon his heels! Lavender pulled up alongside of the _Arabella_ and deliberately made the boat fast. "We got to act as though we haven't found the knife, y'see," he warned. "As though we were going just swimming." In her eagerness to board the _Arabella_ Sidney stumbled. Lavender had to clutch her to keep her from tumbling into the water. "Oh!" They both cried in one sound as they clambered to the deck--for the knife was gone! "Well, _that_ means they'd been on the _Arabella_. Jed Starrow dropped that knife and he missed it and came back to look for it!" "Lav, I believe they've hidden their treasure on the _Arabella_!" Sidney still reverted to the more romantic terms of buccaneering. "Let's look for it now!"