The depiction of unhappiness in marriage in this film, with pettiness and the incredibly bitter things a young couple say to one another, seems very realistic and well ahead of its time, though it isn't always a joy to watch. There are also several other things that you didn't see a whole lot of in films in 1949, including adultery, abortion, suicide, and lesbian flirtation. The plot to the film isn't stellar but it's interesting, and Bergman's use of flashbacks and nonlinear storytelling is effective. He also gets a few very, very nice shots in during the second half, probably the best among his early work, and the film is well worth seeing for those alone.
The Swedish author/painter August Strindberg is referenced directly in this film, and indirectly in its themes of marriage and adultery. In the introduction to the 1960 book which published four of the screenplays from a fantastic string of movies he made over 1955-58, Bergman said "In my own life, my great literary experience was Strindberg. There are works of his which can still make my hair stand on end - The People of Hemsö, for example." Strindberg depicts people in realistic ways, showing both their virtue and vice, and how they tend to look out for themselves first, and I think that is what Bergman was going for here as well.
This is reflected first and foremost in the film's annoying male characters. Early on we see the cruelty of the officer (Bengt Eklund) when he tortures a snake by putting in on a swarming anthill. Later he's casually informing his lover Ruth (Eva Henning) that he's actually married with children, and still later, in front of both her and his wife, calmly stating that it's perfectly natural for him to have both of them (to which his wife just laughs and exits, which is a nice little moment). The cruelty of his reaction when he finds out Ruth is pregnant drives home how base a man he is, even though he tries to come across as a proper gentleman. Of course, Ruth doesn't end up with him, she marries Bertil (Birger Malmsten), a man who is stingy with his money, tenderness, and affection. The scenes they have in the cheap hotel room, alternating between bickering and bantering, are excellent.
In a parallel, loosely connected story, a woman named Viola (Birgit Tengroth) is preyed on by her sleazy psychiatrist (Hasse Ekman), who tries to use the power of his office to get control of her. Later she runs into her old friend Valborg (Mimi Nelson), and as the two are drinking in her apartment, Valborg begins plying her with alcohol and making unmistakable overtures.
The common theme is people moving from one lover to another, or attempting to anyway, and seeking others out in very selfish ways. None of these characters are pure and virtuous or even likeable. Even when the psychiatrist says that he always wants to be there to protect Viola, the words ring hollow since we see how this is likely just an episode in a string of episodes for him. These themes would recur for Bergman in various forms over his career.
Bergman was really coming in to filmmaking form at this point in his career, and one truly fantastic scene takes place on the train where Bertil sees his reflection through smoke, light and shadow as the car jostles along in the night, and Ruth approaches down the corridor with curtains billowing inward. It's brilliant. In another great moment on the train, a cabin full of people drinking pull their shade down on the night, which Bertil had suggested doing earlier to avoid looking at Germans begging for food in the station, and we see the ruins of buildings from the war in the reflection. The flashback to Ruth's younger days as a dancer also provides a welcome bit of lightness and joy, but it's another dark one, a suicide, that is memorable. He films it as just a ripple in the water, a subtle, masterful sequence that shows isolation as well as pointing out that all of our lives are simply small ripples of the water, then gone.
