A man named Tim Templeton tells a story about his imaginative seven-year-old self and his parents, Ted and Janice. One day, Tim is surprised when an infant wearing a business suit arrives at his house in a taxi, and Ted and Janice refer to him as Tim's little brother. Tim is envious of the attention the day-old baby receives, and suspicious because of the infant's clothes and the strange behavior he exhibits around Tim, but his parents are oblivious. Soon, Tim learns that the baby can talk like an adult, and he introduces himself as "The Boss". Seeing an opportunity to get rid of him, Tim decides to use a cassette tape to record a conversation between Boss Baby and other toddlers who are at Tim's house for a meeting, under the guise of a play date in the eyes of the parents. In this meeting, Boss Baby explains that puppies have been receiving more love than babies and is in search of a new file containing evidence of a new puppy from Puppy Co., a company that launches new products for dogs, intends to release. Before they can finish, they catch Tim spying on them. A chase ensues, and Boss Baby threatens to tear up Tim's favorite stuffed animal, Lam-Lam. Tim tries to slingshot Boss Baby out of a window, but is caught by his parents, and accidentally slingshots the cassette tape outside of the house before it is destroyed by a passing automobile. With no evidence to support him, Tim's parents ground him until he becomes friends with Boss Baby. Boss Baby apologizes to Tim and has him suck on a pacifier that transports them to Baby Corp., a place where infants with adult-like minds work to preserve infant love everywhere. Boss Baby explains that he was sent to see why puppies are being loved more than infants and that he has infiltrated Tim's residence because his parents work for Puppy Co., which will unleash the new puppy on a pet convention in Las Vegas. Boss Baby remains intelligent by drinking a "Secret Baby Formula", which enables a baby to act like an adult; however, should a baby not drink it after a period of time, he or she becomes a regular baby. When they overhear Boss Baby's boss threatening to fire him for not bringing in information, which would strip him of his formula and strand him at the Templetons, he and Tim agree to work together to prevent that.