The only way to get away with murder is when revenge is the motive. It’s the only true emotion that allows us to contemplate how not to get caught. In order to feel revenge one must feel loss, it’s during that period of loss a moment of genius is revealed. In a quiet comfortable home tragedy befalls, and a Mother not wanting to forgive or forget has her period of genius which is fueled to set wrongs right.
Unless you have explored this as a psychological fact, or you have touched the writer's heart; that place when truth rings loud and clear, I'd give your premise some serious thought. Thoughtful writers do not use words like "only, must, us." You don't know "only." A bit too off-putting for the thinker. Were "Genius" a product of loss I'd be a bloody genius, and I'm not. Listen to me, I find it best to write to explore and learn, perhaps a journey of self-discovery, thus allowing your audience to learn for themselves; to discover for themselves. Preaching is the perfect way never to be produced. I would rewrite this as it is strictly the case with your characters and your characters alone. That would be understandable. And fabulously interesting. To suggest that choices and consequences for others is a rather stinky pile (which I don't think was really your intent). I tend to think, as IMR, that punctuation and being more explicit, suggesting that this is the case with the characters in your play; the phenomenal obstacle to overcome. Don't try to reach beyond the third wall—let your characters do that. One last thing: NEVER tell, SHOW. BTW, I learned that right here in this forum almost two decades ago. I was nurtured on this forum, and without this forum I don't believe I'd be the writer I am today. Good luck and happy writing, ecw