Truth be told since his own ordeal, Stannis has still not been at his best. He certainly would not embark on such a rescue mission, lest he cause more grief for the captors. Be that as it may, that doesn't mean that he is not going to help out a friend. Particularly when the man had done for much for him to begin with.

Though, if Justice had hoped that he might help with social interactions, he will find that is far from the case.

"I would speak, were I you and choose your words wisely. In some realms, liars have their tongues removed."

It's a statement of fact, and hopefully one that will have the right effect. While he certainly will not be taking justice into his own hands, he knows well enough that a frightened man is a weak man.