At the end of a pleasant day on the island, the Bobbseys again went on board the houseboat for supper.
"We'll watch sure to-night," said Bert to Harry, as they got ready for bed. "We won't go to sleep at all."
"All right," agreed the country cousin.
It was hard work, but they managed to stay awake. When the boat was quiet, and every one else asleep, Harry and Bert stole softly out of their room and went to the passageway between the dining-room and kitchen.
"You watch from the kitchen, and I'll watch from the dining-room," Bert told his cousin. "Then, no matter which way that rat goes, we'll see him."
"Do you think it was a rat?" asked Harry.
"Well, I'm not sure," his cousin answered. "But maybe we'll find out to-night."
"We ought to have something to hit him with, if we see a rat," suggested Harry.
"That's right," Bert agreed. "I'll take the stove poker, and you can have the fire shovel. Now keep very still."
The two cousins took their places, Bert in the dining-room, and Harry in the kitchen. It was very still and quiet on the Bluebird. Up on deck Snap, the dog, could be heard moving about now and then, for he slept up there.