My question involves labor and employment law for the state of: California

My experience in the industry with a leading company was well respected and had achieved many milestones. I resigned from this company for personal reasons and began my own operation. Within months, I was contacted by the biggest vendor in this industry with the intention on entering the direct market. The position that was offered was to build and restructure the company to obtain these goals. I was instructed and given access to anything I needed to make this happen including operation and strategic roles. After traveling and observing what I felt were the obstacles, I reported what was required and identified what needed to be addressed in order to reach these goals. This included identifying my direct higher up as the problem source and lack of leadership. Within a week, I received my termination notice from this person and was not given a reason. I felt somehow my action of identifying his role made for this person to pull rank and gut feeling it was maybe set up in order to "use" my industry knowledge in order to get insight on the operations of a leading company in which previously had played a big role in growing. As I come to dust myself off, I face a discredited image to my performance and character within the industry and having a hard time clearing my name. I feel I can't go on a negative path and open myself to a defamation accusation in doing so. I'm screwed. Understanding the at will position of an employer, I do have a signed hiring agreement which states my role which in the line of work that I do, pertain to "seasons" in which clearly would need years of commitment on my part to obtain what was needed of me. Now I can beat my sympathy drum and say I put aside and closed my newly opened business and reputation but know I don't have a legal stance for a fight. Will my job description and projects that I began during my tenure allow for any legal action defending what I feel is a wrongful termination?

Thank you in advance.