Gabe and his family live on an army base out on an island, and he attends a military school where he is bullied for being easily scared. He is humiliated when he fails the final stage of a training exercise his class was to complete - making him the only one that won't receive an award from the school. His teacher warns of an outbreak of headlice, and as Gabe passes the school infirmary, he sees a classmate writhing in pain and scratching his head. Gabe also hears a high-pitched noise that no one else can hear. At home, Gabe's brother Georgie shows him how to use a heat sensor app on his tablet. Gabe's father tries to check the kids for headlice, but they discover that their nit comb and medicated shampoo have been mysteriously sabotaged. When they go to the pharmacy to get more, it's been vandalized and its entire stock of headlice medication destroyed. Gabe repeatedly hears voices whispering about "a war."
At his school's prizegiving ceremony, Gabe hears the voices again and realizes that it is the headlice. They were not saying "a war", but "awards." He tries to warn everyone to leave but it's too late - they are all infested with headlice and start scratching and convulsing. Gabe escapes into an empty classroom along with his teacher, friend Frankie, and bully Rocky. He tells them that he can hear the headlice, and knew they were about to attack. The teacher tries to call for help but is infected when the headlice attack her phone. Gabe and the girls run to the school nurse's office, using the heat sensor to check for invading lice. They realize that there are two large containers of anti-lice shampoo in the office, and that the lice want to attack and destroy it.
Georgie also turns out to be safe, but the girls are swiftly infected by the lice. Gabe must face his fear of enclosed spaces to crawl through air vents; he pours the shampoo into the school's sprinkler system and activates it, curing everyone who was infected. The following day, the school is fumigated and Gabe applauded as a hero. However, he is haunted by the screams of the dying lice and feels regret at killing living creatures - saying that, like the humans, they were just trying to survive. He hears the headlice whispering "revenge ..." and is horrified to see from the heat sensor that they have infected a cat that's approaching the school.
The Curious is seen at Gabe's school and picks up Georgie's infected baseball cap. It puts the cap on on over its hood and begins scratching.
This episode contains examples of:
- The Bully: Rocky
- Here We Go Again!: The episode ends with the headlice returning and plotting vengeance.
- Masculine Girl, Feminine Boy: Gabe and Rocky. Seemingly also Gabe's parents, since his mother is a soldier and his father stays at home.
- Missing Mom: Gabe's mother is also in the military and frequently away from home.
- Shrinking Violet: Gabe is one due to general shyness and all the bullying he experiences at school.
- Stern Teacher: Gabe's teacher is this (given that she's also an army instructor), but she is understanding when he fails the assignment due to his fear of enclosed spaces.
- What Happened to the Mouse?: Although we see Gabe use the shampoo to stop the head lice at the school, it is unknown what happened to everyone at the emergency services call centre who was being attacked by the head lice.
