I made a promise that if anyone set me free, I would make him very rich.
斜体部分是同位语从句。我们可以用“主表”检验一下，是不是同位语。如果主表成立就是同位语：
My promise is that if anyone set me free, I would make him very rich.
That if anyone set me free, I would make him very rich is my promise.