When a mysterious yellow envelope arrives at Hollyhock House, it causes quite the hubbub. It’s addressed simply to “the greatest grandmother in the world.” The trouble is, there are a lot of grandmothers, great-grandmothers, and even a great-great-grandmother living at Hollyhock House. So who is the grandmother? Whether your grandma is a Bubby, a Bibi, an Abuela, a Nai Nai, or a Grammy, has something for everyone to enjoy: a zany tale full of mischief, mystery, and plenty of grandmotherly love.