In the sentence "The law doesn’t hold good," "hold good" means that the law is not valid or enforceable. "Hold good" is an idiomatic expression that is often used to mean that something is still effective, valid, or applicable. However, in this context, the opposite is being implied - that the law is no longer effective or valid. Therefore, the sentence means that the law is not working as it should, and perhaps it is not being followed or enforced properly.