Gertie is the littlest yak in her pack, feeling stuck in her smallness. She wants to grow up and have BIGNESS and TALLNESS, with the hugest of hooves and humongous horns too! Because there isn't anything a BIG yak can't do. So Gertie devises a growing-up plan. She eats her veggies, exercises every day, and reads lots of books. Still, she isn't any bigger. But when the other yaks come calling for Gertie to help them with a daring and dangerous task, could it be because it's something only a small yak can do?