Relationship Between a Principal and an Agent

Karen is shopping at Big Mart. She has with her an umbrella which is the same brand Big Mart carries. When a Big Mart employee, Steve, sees her leave with the umbrella without going through the checkout lane, he asks her to come back into the store. Steve says that he thinks Karen is shoplifting the umbrella. Karen tells him that she has had the umbrella for years and shows him marks of wear and tear. Steve apologizes and tells Karen she is free to go. Can Karen successfully sue for false imprisonment or defamation? From what you have learned about the relationship between a principal and an agent, analyze whether Steve or Big Mart could be liable because of Steve's actions.