Big Sister has been the only child for four years, soaking up all of her parents’ attention-until now. Excited at first, she soon realizes that life with a new baby isn’t what she expected. Bottles, diapers, and tired parents replace the laughter and routines she once knew.

As her overactive imagination runs wild, she starts feeling left out, confused, and even jealous. She overhears a conversation about her “mysterious” illness, sparking a journey of self-discovery. But despite the changes, she slowly warms up to her little brother, realizing that love isn’t divided-it grows.