Terence Davies adapted and directed the film, based on the play by Terence Rattigan, with a complete immersion in the viewpoint of his lead character. This is a small story, set in 1950, but the emotions are epic, and Davies expresses those emotions with an epic treatment — with a loud string section on the soundtrack, dreamy takes and scenes that crystallize in just a single line of dialogue, suggesting the power of memory to compress events into moments.
Weisz plays the 40ish wife of a 50ish judge who meets a 30ish young man (Tom Hiddleston), a former World War II pilot in the RAF. Her discovery of physical love cannot be ignored, even though she realizes that this young man, for all his surface bonhomie, has been dead since the war. The war was his great revelation, just as love is hers.
If I tell you this film is a study of one woman's torment, it might make The Deep Blue Sea sound unappealing, but it's riveting from beginning to end, because virtually at every moment, someone's entire life is in the balance. On most of those occasions, we're watching Weisz, but sometimes we're watching Simon Russell Beale as the husband, as he uses every ounce of British reserve, and every aspect of 1950s repression, to contain an impulse to burst into tears.
Weisz's performance, from moment to moment — in merciless close-up and long takes — is innovative, truthful and revealing. Her innate appeal helps, as well. I imagine most women watching will identify with her, just as most men will watch with the frustrating conviction that if only they were allowed into the movie, she could get rid of both men and finally be happy.