David Cronenberg’s Eastern Promises begins with some graphic, grisly violence, leaving no doubt that there’s more to come later on. But it is also a strangely tender film, and an oddball thriller full of peculiar undercurrents and unexpected sensitivities. And strangenesses of several sorts makes it into a surprisingly edgy and compelling experience. It’s a Russian mafia tale in a British setting, and the violence goes more or less with the territory. But it’s also about Russian exiles, and one of its chief characters is an Anglo-Russian midwife, Anna (Naomi Watts), whose concern for the newborn child of a teenage prostitute (who dies giving birth) draws her into the milieu of the local Russian gangsters. The mafia includes the émigré restaurateur Semyon (Armin Mueller-Stahl) and his extravagantly erratic son Kirill (Vincent Cassel). But even more central is Nikolai (Viggo Mortensen), their chillingly efficient chauffeur and jack-of-all-dirty work, who shares the crime family’s background in Soviet-era prisons. The potential for gruesome melodrama does not go unattended here, but the confrontation of half-crazed earnestness (Watts) with half-concealed menace (Mortensen in one way, Mueller-Stahl in another) is only part of the story. In the hands of Cronenberg and screenwriter Steve Knight, the tenderness and the violence may be opposite sides of the same coin.