The Secret of Blood: A biographical film about a Czech doctor, Dr. Jánský. The athletically inclined medic Jánský successfully completes his studies. He wants to become a surgeon, but finds himself in Professor Kuffner's psychiatric clinic, where, together with his colleague Kozdera, he tries to uncover the connection between blood clotting and mental illness. They make the surprising discovery that human blood can be divided into four groups and thus prevent it from clotting during transfusions. However, Jánský's discovery is met with misunderstanding by the Czech medical community...