Eleven-year-old Leo is an "armchair adventurer," preferring adventures in books or video games over real-life experiences. Unlike his little sister Lizzie, Leo is not a risk taker. So when his family visits Grandpa on Heron Island, Leo finds all kinds of dangers to avoid -- from the deep, dark ocean to Grandpa's old barn that looks like it might collapse. But nothing on the island is more fearsome than Grandpa himself -- Leo has never met anyone so grumpy! Mom says Grandpa is still grieving the recent death of Grandma, a beekeeper beloved by everyone on the island. When Grandma's beehives go missing, Grandpa vows to track down the sticky-fingered thieves, and soon Leo finds himself exactly where he doesn't want to be: stuck on an adventure with risk-taking Lizzie and reckless Grandpa -- plus a stray kitten named Mayhem!