Carrie has dedicated her career to the family business. When her sister announces that she is getting married, an old will is discovered stating that ownership of the company goes to the husband of the daughter who marries first. Everything Carrie has put into the company is now threatened if she doesn't manage to get married before her sister.
The family's incomprehension that Carrie is devastated is completely incomprehensible. The solution (even if it is supposed to be "happy") is also an injustice if you ask me.
