A likeable young girl who's burnt her family home to the ground.

A man with no memory of the night he killed his wife.

A teenager whose visions and voices have had murderous effect.

One question binds these and others from the casebook of Britain's leading forensic psychiatrist: Why?

What drives a person to commit seemingly inexplicable crimes?

Dr Duncan Harding is the person the police and the courts turn to for answers. An expert witness, he must try to establish a defendant's mental state and motivation. And their fitness to stand trial.