The book chronicles almost 300 in-season changes of managers in the major leagues since 1900. It elaborates on the circumstances that led to the change, whether it was a firing or a resignation and includes, in many cases, remarks of the dismissed manager, the manager who replaced him, and the executive (owner or general manager) who orchestrated the change. It then examines how the team fared under the new manager. The central purpose of the book is to study the effects of the changes: how many had a positive impact, how many had a negative impact, and how many had little if any impact on the team's won-lost record.