The Templeton brothers—Tim and his Boss Baby little bro Ted —have become adults and drifted away from each other. Tim is now a married stay-at-home dad. Tim and his wife, Carol,  live in the suburbs with their super-smart 7-year-old daughter Tabitha and adorable new infant Tina. Tabitha, who’s at the top her class at the prestigious Acorn Center for Advanced Childhood, idolizes her Uncle Ted and wants to become like him, but Tim, still in touch with his overactive youthful imagination, worries that she’s working too hard and is missing out on a normal childhood.

When baby Tina reveals that she’s—ta-da!—a top secret agent for BabyCorp on a mission to uncover the dark secrets behind Tabitha’s school and its mysterious founder, Dr. Edwin Armstrong, it will reunite the Templeton brothers in unexpected ways, lead them to re-evaluate the meaning of family and discover what truly matters.