>Jens, a 16-year-old boy, goes on a camping trip with his friends to a cabin. One of the girls is Lisa, Jens’ crush from the previous summer who moved after her father got a job in Oslo. During a game of Truth or Dare, Jens is dared to kiss Lisa and afterwards the two have sex for the first time. Inside Jens’ testicles lives a society of sperm cells. A young sperm cell named Simen Sprut is ostracised due to not having any interest in taking part in the race to the egg. His only friend Cumilla however, tries to get him to take an interest. Meanwhile Jizzmo, an entrepreneur sperm cell, creates an armoured suit called the Ejaculator 9000 which allows him to fight through anything that will prevent him from getting to the egg, including killing other sperm which he demonstrates by brutally killing a worker.
>During Jens’ first ejaculation, Jizzmo cuts open the condom which allows him and other sperm cells to enter Lisa’s vagina. Simen upsets Cumilla when he holds her back from entering Jens’ urethra. Meanwhile, Jens and Lisa have sex again. However, due to Jens being tired from the previous intercourse ends up penetrating Lisa’s anus. This time, Simen and Cumilla, along with their teacher Professor Saltsmak and classmate Etterskvett (Aftersquirt) enter the urethra but unfortunately end up in Lisa’s rectum. There, they meet an e-coli who guides them to Lisa’s system where they travel through her bladder and manage to swing on her pubic hairs into her vagina while she is urinating. However, Etterskvett ends up falling to his death.
>Lisa applies spermicide which kills many of the sperm inside her uterus, including Saltsmak. Meanwhile, a trio of gangster sperms led by Egon Olsæd who are on a mission to enter the egg and become triplets try to get the spermicide to kill Jizzmo but he escapes and instead kills Egon’s friends Benner’n and Bjell. Jizzmo then tries to kill the other sperm cells but is stopped by Egon who causes Jizzmo’s suit to self-destruct, sacrificing himself, killing the spermicide and allowing the other sperm cells, including Simen and Cumilla to swim to the egg.
>Jens and Lisa go on a walk and Lisa expresses her frustration to Jens for not being able to have an orgasm from when they’ve had sex. The two have sex against a tree and as soon as Lisa ejaculates, a beehive falls on Jens’ pelvis who ejaculates in it. The bees chase Jens along with Lisa and the two end up falling down a hill. In Lisa’s uterus, the turbulence causes the egg to bounce around, killing the other sperm cells and leaving only Simen and Cumilla. However, a still-living Jizzmo attacks them and is finally killed when he bites off Cumilla’s tail and is crushed by the egg. Simen and Cumilla enter the egg together.
>Six weeks later, Jens and Lisa go to a clinic to get an abortion pill where the gynaecologist explains through song that they should take time to plan for a family if that’s what they want. The film ends with Jens suggesting a movie marathon with Lisa as the abortion pill will take two days to work.