University professor Josef Held has never recovered from the loss of his beloved wife - and has no intention of ever letting anyone new into his quiet, safe world. It is a world where the clock ticks steadily in his mathematics classroom, even as the sinister beat of Nazi soldiers'' boots threaten to drown it out.Terrified, Josef tries to keep his eyes on the ground as Jews across the city are forced into ghettos. But then Michael Blum, his most reluctant, infuriating pupil, tells Josef Jews like him will no longer be allowed to study at all. Josef can ignore the situation no longer. And, after the shock of seeing his neighbour killed on his own doorstep, he offers Michael a place to hide in an impulsive act of courage.