Detective brothers Frank and Joe work to debunk a time travel machine in the eighth book in the interactive Hardy Boys Clue Book series. Bayport Elementary is almost ready for the annual science fair--it's all down to the final touches. Frank and Joe have collaborated on a detective helmet. It's the perfect lie detector--just place it on a suspect's head and the bells and whistles will tell you when they're lying. But not everyone is as prepared for the big fair. Their good friend Phil has designed a time machine he calls the Time Warp Wonder. He just needs to figure out how it works first... Phil uses Chet's hamster as a test subject. And the machine really does make the hamster disappear from the cafeteria! It's just that Phil isn't sure where the hamster went or how to get him back. Frank and Joe are not so sure the hamster went back in time. They have a feeling their Clue Book will be more help to Chet's hamster than Phil's calculations. But the brothers start questioning their instincts when they receive pictures of the hamster in different time periods; dressed as caveman with the dinosaurs, suited up in armor in the middle ages, in a top hat watching Abe Lincoln give a speech. Could Chet's hamster really be traveling though time? It's up to the Hardy Boys--and you--to find out!