Sisu is simple, 91 minutes of gritty action. Finnish writer-director Jalmari Helander has a track record of pulpy thrillers, namely Rare Exports: A Christmas Story and Big Game. With Sisu, the experience has been pruned to an unpretentious bloodbath. It is a knowing throwback to the gleeful adult action of the 1970s and 80s, with its chapter titles ('Chapter 2: The Nazis') and bombastic score (by Juri Seppä and Tuomas Wäinölä).
Sisu untranslatably means relentlessness, we are informed at the…