Representing Calvin in his lawsuit against the department store for false imprisonment and defamation.

Summary of event:

Calvin Worker was visiting a local department store. He decided that he really like a pair of expensive jeans and went into one of the store's dressing rooms to try them on. Sara Eagleye, a salesperson at the store, watched Calvin carefully. He was dressed in shabby clothes and did not seem the type who could afford the jeans he took into the dressing room.

Sara decided that Calvin was up to no good. She locked the dressing room door so Calvin could not get out. She then called the store's security guard to report the situation. The guard arrived in about 5 minutes, opened the locked dressing room door and demanded to know why Calvin had the jeans. Calvin explained that he had intended to buy the jeans until he was locked in the dressing room and showed that he had cash to do so before storming out of the store.

Question is :

How can I argue that Calvin should be successful in his lawsuit against the department store for false imprisonment and defamation.?