Behind every thought, action and experience there lies a chain of biological and environmental causes, stretching back from the moment a neuron fires to the dawn of our species and beyond. Nowhere in this infinite sequence is there a place where free will could play a role. Without free will, it makes no more sense to punish people for antisocial behaviour than it does to scold a car for breaking down. It is no one's fault they are poor or overweight or unsuccessful, nor do people deserve praise for their talent or hard work; 'grit' is a myth. This mechanistic view of human behaviour challenges our most powerful instincts, but history suggests that we have already made great strides toward it: where once we saw demonic possession or cowardice, for example, now we diagnose illness or trauma and offer help. Determined confronts us with our true nature: who and what we are is biology and nothing more. Disturbing and liberating in equal measure, it explores the far-reaching implications for society of accepting this reality. Monumentally difficult as it may be, the reward will be a far more just and humane world.