Billy, Jessintha and Cookie go and stay with their boring Grandpa Will and Grandma Irene during their school summer holidays. To get their attention, Grandpa Will and Grandma Irene take them on an exciting magical adventure to Tamu Valley. Their bond is tested when Grandma Irene is bitten by a poisonous spider due to Billy's silliness. She doesn't have long to survive and the only thing that can save her is -- 'The Magnopeus medicine'. Can Billy, Jessintha and Cookie save their Grandma Irene in time?