Eleven-year-old Leo is an "armchair adventurer." This, according to Dad, means he'd choose adventures in books or video games over real-life experiences. Unlike his little sister Lizzie, Leo is not a risk-taker. So when he, Lizzie, Mom and Dad leave the city to visit Grandpa on Heron Island, Leo finds all kinds of dangers to avoid — from the deep, dark ocean to an old barn on the verge of collapse. But nothing on the island is more fearsome than Grandpa himself — Leo has never met anyone so grumpy! According to Mom, Grandpa is still grieving the recent death of his wife, a beekeeper beloved by everyone on the island. Despite Leo's best efforts to avoid it, adventure finds him anyway when Grandma's beehives go missing in the dead of night. Infuriated, Grandpa vows to track down the sticky-fingered thieves himself...  with risk-averse Leo and danger-loving Lizzie (plus a kitten named Mayhem) in tow.