Justice and Grace

This is a follow up to the Christian Service post a few days back.
I am trying to get a handle on what the relationship between justice and grace is supposed to be for the Christian. We are called to both love justice and be full of grace, yet grace overrides justice in some sense. We might think that we ought to always pursue grace, but this does not seem right. It seems at least that when we are looking out for others we ought to seek justice for them. We are to seek justice for the widow and orphan. Are we to seek grace instead for their oppressor? Perhaps this is the best approach -- the others-centered default approach:
To seek justice for others, but not for oneself; and to seek grace for one's oppressors but not for the oppressors of others. (perhaps there is some parallel with forgiveness here)
I don't know. This is tough. I would appreciate thoughts.