It's summertime, and Greg Heffley is heading to the beach for vacation with his family, but Greg quickly finds himself caught in the middle as the two halves of his extended family come together in a tiny beach house in the sweltering heat. The secret ingredients behind Gramma's famous meatballs have been closely guarded for years, and Greg hopes she will pass it on before she passes away. But tensions soon start to rise between family members, and Greg worries he's only going to stir the pot.