K.C. tries to convince her parents that her brother, Ernie, who is a genius with computers but pretty clumsy at everything else, is ready to become a spy. However, Craig and Kira have a different plan and introduce them to their new little sister, Judy - a sophisticated humanoid robot disguised as a precocious 10-year-old.

Ernie and Judy must travel to NYC for the Central Park Spooktacular to intercept an evil wolf serum, but their mission is interrupted when they run into “Jessie’s” Emma and Zuri at the party. Meanwhile, Marisa and K.C. throw their own Halloween bash back at the house and K.C. decides to dress up as a spy to impress the new boy in school, River.

When a former foe needs the Coopers' help, the family has to decide if they can face the consequences of aiding the enemy.

Six months no longer part of the Organization, the Coopers have to live their lives without being spies. That changes their lives forever. But when K.C finds out that Ursula has been torturing them, the Coopers have to strike back to get Judy back and to eliminate Ursula.

When Kira forbids K.C. from spending time with her newfound cousin Abby, the teenage spy finds a way around her mom's orders.

Kira reluctantly agrees to help K.C. reunite Abby with her mother Erica, who has been hiding from The Other Side and The Organization for several years.

When Darien is mysteriously injured in an accident, K.C. tries to figure out who is behind it. Meanwhile, Craig becomes head of security for a vice-presidential candidate.

When K.C. learns Erica and Abby are working with the head of The Other Side to carry out an evil mission at the Presidential election party, the Coopers must act fast to stop the enemy agents.