On the strength of one of his stage-plays, The Death of Punch, Ingmar Bergman was invited to join Svensk Filmindustri's script department in January 1943. As a so-called "script slave" with, for the first time in his life, an office, a desk, and a regular salary, he daily read, rewrote and rejected or recommended a range of possible screenplays for Svensk to produce. Not surprisingly, his own material was often included among the projects on offer, and eventually he struck lucky with his script for Torment, directed by Alf Sjöberg in 1944. It was well received, and Bergman was entrusted with Crisis, released in 1946, his first film as director. This was not a success and the next Bergman proposal, Sentimental Journey, was shelved. Four years later, it became Summer Interlude.

Its origin was a short story, Marie, written "just for fun" in 1937, which celebrated a tentative summer romance between the 16-year-old Bergman and a shy island girl who "lived with her parents in a strangely unfinished house, a little like a drama by Chekhov." As a memoir it embodied three main themes: the fragility of a first love affair, the special magic of a summer on the Swedish archipelago, and the fear that, under the threat of war, the world was about to be irretrievably changed. When Bergman went to Svensk he made several attempts to expand his text into a screenplay, but it became "entangled in itself and filled with flashbacks which I couldn't find my way out of. Then Herbert Grevenius came to my aid, chiselled away all the superfluous episodes and restored the original story."

Grevenius was one of Sweden's foremost drama critics, who followed Bergman's career with great interest and loyalty over the years. It was thanks to Grevenius that Bergman was appointed head of the Helsingborg City Theatre in 1944, his theatrical productions forming an extraordinary parallel to his film work, with members of his cast often transferring from stage to screen. Credited co-writer on at least five of Bergman's early scripts, Grevenius brought a keen ear for dialogue and "a certain orderliness of thought" that helped to discipline the director's chaotic workload.

Another vital contributor to the triumph of Summer Interlude was the cinematographer Gunnar Fischer. Veteran of some thirty films as assistant or leading cameraman since 1935, his first with Bergman was Port of Call (1948), where Fischer's conjury with rich shadows and exuberant theatrical lighting was much to the director's taste. Fischer was to film twelve of Bergman's scripts, including, most famously, The Seventh Seal and Wild Strawberries, before their parting of the ways in 1960. The tentative use of sunlight in To Joy (1950) seems to have been a revelation to them both, and Summer Interlude, filmed on the island of Smådalarö, became an almost unprecedented visual symphony of water, sky and landscape, and a yearning recollection of vulnerability and brief perfection.

Bergman also pays tribute to Maj-Britt Nilsson, whose selection for her previous performance in To Joy followed, ironically, her role in The Girl from the Third Row (1949), made by Bergman's actor-director rival Hasse Ekman as a riposte to Prison (1949). "The camera catches her with an affection that is easy to comprehend," says Bergman. "She embraced the girl's story in Summer Interlude and lifted it higher with her brilliant mixture of playfulness and seriousness." And he adds: "The film became one of my happy experiences—it was the first in which I felt I was functioning independently, with a style of my own, making a film all my own, with a particular appearance of its own that nobody could copy..."

For today's viewer, what makes the film such a pleasure to watch is the assurance and intricacy of Bergman's new-found style. It is an adventure on several levels, crowded with hints and meanings, no detail without its own resonance. Note, for example, the use of the little statuette on Marie's dressing-table, or the fact that Marie gradually removes her mask of make-up until her real features confirm she has found herself again. True, the make-up is professionally restored for the final scene, but here the close-up of the shoes illustrates the strides that Marie and David have taken towards reconciliation. And alongside Bergman's habitual fondness for mirrors it is a film about windows, through which lost opportunities can be glimpsed before the blinds are unfurled.

Perhaps the most elusive meanings relate to the diary, which causes understandable confusion by being Henrik's and consequently unknowable since he doesn't share it with us. We have to assume that it tells us as much about Marie as she does (the whole film is told from her point of view), but did she actually read it, and if so, when? And what does she think David will learn from it that she couldn't have told him herself? Why does Uncle Erland suddenly decide to send the diary to her after years of getting her to accept his morbid philosophy ("In the long run, nothing has any meaning")? She asks him but his reply is less than helpful. It remains as much a mystery as Marie's chance encounter with Henrik's aunt who, initially with only three months to live, is apparently still pacing the island thirteen years later.

Those missing thirteen years form a kind of vacuum at the centre of Summer Interlude, undoubtedly due to become some other mystery. That Marie should have been able to forget Henrik, or that she could have submitted to Uncle Erland's clutches in order to construct a wall around her emotions, seems inconceivable and unproven. Clearly the ballet has provided compensation, but as the ballet-master (a Death-figure, according to some) warns her, she only has another eight years before enforced retirement. Try as he might, Bergman can't and won't come up with an all-problems-solved ending: Marie simply promises David that they'll talk. The film is not about easy answers: it's about loss and the search for a long-ago summer when love was without complication. It is, in short, a polished, potent and constantly beguiling rehearsal not only for Summer with Monika but also for the grandeur of Wild Strawberries.