Your brother had been right after all: two biochemistry geniuses in the same marriage was one biochemistry genius too much. Ego had turned fascination to annoyance… and when it came to poisons you were years ahead of forensic state of the art.
Both of you. You were self-aware enough to know that she had been faster, not less ethical, and intellectual honesty forced you to accept that her attempt had been a work of art. Saving your own life had required your utmost brilliance: the approval in your wife's eyes had been as unmistakable as her awareness that it was now your turn to try.
You both knew your egos wouldn't let you involve the police or go away. And anyway for the first time in years you were having fun.