Legal Question in Business Law in California

From these limited facts, it sounds like your partner received the shares pursuant to a contract which he has breached. If that's what happened, you should be entitled to get them back. My answer might be different if I knew more about what happened.

A demand letter from a lawyer might persuade him to hand over the shares. If your former partner refuses, though, you may need to litigate. That may be complicated, depending on the nature of your partnership, how you set up the corporation, how the shares were transferred, how long ago these things happened, and a variety of other factors.

Feel free to contact me directly if you'd like to discuss your case in more detail.

A fairly clear case of breach of contract, but not enough information given even to tell whether the contract was oral or written. Also, making recommendations as to what to do (i.e., whether or not to sue) would require having some information as to the amount of the start-up loan, whether it is secured, whether you or the corporation or both are on the hook for it, and whether the corporation has assets and a successful business or is just sitting there with near-zero assets and prospects. You need to have an initial discussion with a business lawyer with experience in small-business disputes. Also, be careful in describing the other party here as a "partner." That term implies a special kind of business relationship that probably isn't present here.