The unlikely friendship/romance between Mark and Natasha begins when they're thrown together when her mother marries his uncle. Natasha never smiles, says a character. But Mark is assigned by his mother to show her around their suburban town, which he dutifully does. And gradually, she learns to trust him.
There is a sweetness and tenderness that develops between Mark and Natasha, but the causes of her underlying sadness lurk nearby. It would give away too much to provide more detail. So suffice it to say that the movie works well for the most part, portraying two teenagers who both speak Russian but otherwise have very different backgrounds and life experiences, yet come together in a natural and believable way.
The use of Russian with English subtitles is so well integrated into the story that I barely noticed. It looks and feels like an English-speaking film, just one in which the principals speak mostly Rusian.