The melancholy sound of an oboe thrums through the opening frames of Catarina Mourão’s contemplative documentary as the camera moves languorously through a slightly rundown house whose pale blue corridors are smudged with streaks of white paint. Performed on screen by a young soloist, the music floats from room to room, leading us to an older man, his eyes gazing at an intriguing assortment of postcards pasted on to the ocean-coloured wall.

This man’s name is Martim, and these yellowing artefacts tell the story of his extraordinary journey from Portugal to Soviet Russia in 1979. Smitten with socialist ideals, he left Lisbon for the cold climate of Astrakhan on the Caspian Sea in southern Russia, where he enrolled in a course on fishing techniques at the tender age of 15. Martim’s youthful idealism, however, was soon dampened by the harsh reality of living abroad alone. After only a year, relationship troubles and a disillusionment with the communist regime, led Martim to return hastily to his home country.

Besides postcards and photos of Russia taken with his clandestine camera, Martim carried with him a sense of failure and shame. In addition to confronting the past, Mourão’s film also makes possible an intergenerational dialogue between Martim and his son, the young musician seen in the beginning; he also harbours his own secrets. Emerging from their conversation are sparks of understanding and compassion, which constitute the emotional beating heart of the film.

In contrast to these riveting moments, the re-enactments of Martim’s time in Astrakhan feel quite distracting and even unnecessary. Instead of these dramatised interludes, Martim’s experience, as well as his moving rapport with his son, could have been enough to carry the film’s various ruminations.

• Astrakan 79 is at the ICA, London, from 20 September.