Beakman explains what a vaccine is by acting like Edward Jenner. He explains how Jenner created the first vaccine using cow pox. Then Beakman uses a large ball (cell) with holes in it (receptors) and explains how viruses (a cube with pegs on it) attack our cells by attaching to the cell (pegs on virus go in holes aka receptors on cell). Beakman likens antibodies to cowboys ready to fight and explains how the immune system is normally triggered from a virus, unless that virus is too fast, then the body can't catch up. He then explains that vaccines work tricking the immune system into going ahead and making antibodies so that when you really do get sick, you can put up a better fight.

An alien has taken control of the ship, and the crew need to fight it. Spock explains the situation in terms of biology: the ship is the body, the crew are the blood cells, and the alien is the virus.

Thrax holds an evil meeting in which he highlights his successes as a viruses. He illustrates that viruses can cause sickness and even be lethal. Jones, the white blood cell, asks if there is anything he can do to stop the virus, indicating that white blood cells (also known as leukocytes) protect the body from illness, disease, bacteria, and other foreign invaders.

Ralphie's class enters his body to find out what is making him sick. His classmates find bacteria cells in his throat and watch the white blood cells battle the bacteria cells. This clip illustrates the function of white blood cells: to fight infection and disease.

The StoryBots take a trip to the lymph node, where they speak to a white blood cell. They learn about the role that the white blood cells play in protecting a person's body against viruses.