Oliver Twist follows the journey of its main protagonist, the orphaned Oliver Twist, from the workhouse to his eventual restoration to middle class society. While Dickens primarily uses Oliver Twist as a vehicle for advocating social reform in Victorian Britain, he also uses it to illustrate the perceived threat that criminality poses to mental health. This is evidenced in Bill Sikes tortured response to his murder of Nancy when his desolate state leads to his mental decline. The focal point of his spell of insanity in the novel is clearly a direct result of his criminality, and this is indicated by his perception that Nancy’s ghost is haunting him. Fagin is another character who has descended into insanity by the end of the text as punishment for his criminal activities.

'Every object before him, substance or shadow, still or moving, took the semblance of some fearful thing; but these fears were nothing compared to the sense that haunted him of that morning’s ghastly figure following at his heels. He could trace its shadow in the gloom, supply the smallest item of the outline, and note how stiff and solemn it seemed to stalk along. He could hear its garments rustling in the leaves; and every breath of wind came laden with that last low cry. If he stopped it did the same. If he ran, it followed—not running too: that would have been a relief: but like a corpse endowed with the mere machinery of life, and borne on one slow melancholy wind that never rose or fell' (Dickens 388).

'Now he started up, every minute, and gasping mouth and burning skin, hurried to and fro, in such paroxysm of fear and wrath that even they—used to such sights—recoiled from him in horror. He grew so terrible, at last, in all the tortures of his evil conscience, that one man could not bear to sit there, eyeing him alone; and so the two kept watch together' (Dickens, 430).