"Mr & Mrs Smith" begins with a couple seeking marriage counseling. Things between the couple are stale, boring, none of the romance and mystique that they experienced in the first few years of their co-existence in a common household.
Are the Smiths professional assassins in their "real" lives? Or does it really matter? Every married couple will eventually start questioning their marriage after a time. Their story is a metaphor for what happens in a marriage relationship after the fireworks have died down and routine eventually sets in.
The movie follows a pattern of behaviour that generally begins 5 or 6 years after the honeymoon. Whether it's career or hobbies or personal interest, 2 people though pledged to each other can drift apart. After 5 or 6 years of talking to each other, can there be anything left to talk about? As communication breaks down, suspicion creeps into the picture. Suspicion causes a search for "evidence" of wrongdoing, though sometimes the search isn't an active one but rather a putting together of 1 + 1 = 3. Interpreting "evidence" leads to the conclusion of betrayal and here's where the bullets start flying hard and fast. Bullets not necessarily composed of lead and powered by gunpowder, but spiteful words powered by anger which are designed specifically to hurt as much as buckshot. And hurt they do.
The marriage is in a major crisis at this stage. Whether the 2 survive as a couple depends on how fast they recognize that the enemy isn't each other, it's the situation around them. It's essential that they identify what is tearing them apart and they agree to work together to deal with it. Remember that in this movie, the survival of either husband or wife is not in question; rather, we worry about whether the marriage remains intact regardless of the eventual fate of either party.
The climactic battle is purely a dance, set to the staccato rhythms of gunfire. The way the Smiths coordinate with each other, anticipating each other's moves and always, always, watching each other's backs shows a couple that has gone past the vagaries of the communication-interpretation stage (the messy part of a relationship) to the understanding-without-words stage where thought and knowledge are instantaneously shared between the two. That is truly transcendent.
Interestingly enough, like the Smiths, June and I have already been married for 5 or 6 years. Wonder what she's hiding in the oven, I mean besides the Thirsty Hippo?