Three years after trouble in college, Blake Renner and his girlfriend, Sarah Masters Aimee Teegarden, move into a house with a beautiful backyard and a guest house that promises peace. The realtor reveals a single catch: Randy Cockfield Pauly Shore, a drug-addict-turned-squatter, has claimed the guest house and has been hoarding drugs and priceless artifacts. Blake keeps a day job at a skateboard shop run by Shred, while Sarah teaches at a local school. After two months, Randy is still there, and the situation only grows stranger when he finds and keeps a wild possum, turning the yard into a peculiar menagerie that becomes part of the couple’s daily tension.
Blake and Randy exchange tense conversations, sometimes sharing a joint, as the uneasy coexistence drags on and the guest house remains a constant source of disruption. Sarah becomes increasingly annoyed by the ongoing intrusions, and her father, Douglas Masters Billy Zane, does not approve of the relationship, casting a shadow over their plans for the future. Despite the friction, Blake proposes to Sarah, and she accepts, continuing to hope for a normal life together even as family concerns loom.
Six months pass, and Randy persists in living on the property. He stages an orgy, and when Blake tries to intervene he is drugged and an explosive gazebo incident with fireworks disrupts the neighborhood. The chaos escalates into a turf war, with Blake assaulting Randy and getting arrested, then bailed out again. The local cops—corrupt allies of Randy—allow him to obtain a restraining order against Blake, effectively tipping the balance of power in the confrontation.
Randy then infiltrates the couple’s home and injections MDMA into their water bottles, altering behavior and leading to a bout of uncontrolled sexual activity that results in Blake losing his job. With more idle time on his hands, Blake hires a crew to bomb the guest house with pesticides in an attempt to force Randy to leave, but the plan only sends Randy into medical retreat for a while. When Randy is finally gone, Blake and Sarah try to settle into a quieter life with a quiet dinner in the backyard, hoping for peace.
Randy returns with a vengeful gesture, releasing a drug-addicted possum with rabies onto the couple, leaving bites that require rabies injections and sending one guest to the emergency room. The couple then plans their wedding in the backyard, and despite lingering doubts from Sarah’s father, the ceremony goes ahead. During the celebration, Randy slips MDMA into drinks, causing the guests to behave erratically and damage the home. In a tense confrontation, Blake discovers Randy hidden in the attic, and while he drives toward violence, Douglas stops him and fights back.
Blake and Randy are arrested, and Sarah bails Blake out. In a quiet moment, Sarah reveals that she is pregnant with Blake’s son, adding a sense of future amidst the upheaval. Blake eventually finds a new job, and the couple faces a period of separation before they’re called back for questioning about the house. They locate Randy, and a fragile peace is reached as Randy explains that he repaired the damages with proceeds from selling a priceless artifact from his collection and that the house had been owned by his parents. He even shows that he redesigned the guest house into a room for their baby and expresses a genuine desire for a family to live there.
Randy leaves, and the newly-weds move back in to raise their son. They receive a video chat from Randy, now partying on a yacht, who promises his companions will come to the guest house again. Blake and Sarah firmly state they will not allow him to squat in the guest house, choosing their own family’s future in the home they built together.
