The young woman, Gemma, and her fiancé, Tom, are initially excited at the prospect of finding their first home together. However, their excitement turns to confusion when they meet the bizarre real estate agent who takes them to a strange housing development called "Yonder". The houses in Yonder are all identical and eerily quiet, with no signs of life or anyone around.
After being shown around by the agent, Gemma and Tom find that they cannot leave Yonder and are trapped in this strange, unnerving world. As they try to find a way out, they discover that something sinister is afoot in Yonder. They hear a strange noise and follow it to find a box with a young child inside. They are instructed by a note left with the child to raise it until it reaches maturity and then they will be released.
As the days pass, the couple becomes more and more isolated, with no communication from the outside world, no food deliveries, and no way out. The strange child, who they name "Jesse", grows rapidly and starts exhibiting unusual behavior. Jesse appears to be a blank slate, with no facial expressions and the ability to mimic everything Gemma and Tom do.
After attempts to escape fail, Gemma and Tom become increasingly desperate, and their relationship begins to fray. They argue about whether to accept their fate or keep fighting, with Gemma wanting to keep trying to escape and Tom becoming more resigned to their situation.
Vivarium is a surreal, unsettling film that offers a dark commentary on the idea of the perfect family and suburban life. It is a disquieting exploration of the human psyche and the lengths we will go to survive.