Chestnut follows the story of Sarah, a recent college graduate who is trying to navigate life after school. She meets and becomes romantically involved with both Mark and Rachel, a couple who are in an open relationship. Sarah is initially hesitant about dating a couple, but she soon finds herself drawn to both Mark and Rachel in different ways.
As the summer progresses, Sarah must navigate the complexities of being in a relationship with two people at once. She grapples with her own feelings of jealousy and insecurity, as well as societal judgments about non-traditional relationships. Through it all, Sarah learns more about herself and what she truly wants in a partner.
The relationships between Sarah, Mark, and Rachel become increasingly complicated as emotions run high and boundaries are tested. As the summer comes to a close, Sarah must make a decision about where her heart truly lies and what kind of relationship she wants to pursue moving forward.