Frank and Joe Hardy are super-psyched for their school trip to Lake Poketoe. Along with their friends, they can't wait to go tubing, make s'mores, and take nature walks. And Joe is particularly excited to try out his brand-new water skis during the trip!

But when the group tries to head out for their first day of boating, Joe discovers his skis are missing! Who could have taken them? And how could they have disappeared without anyone noticing? With time running out on their trip, can Frank and Joe figure out who the sneaky ski thief could be?