This article claims that Mary Shelley belonged to a group of writers and intellectuals who contributed to bring about reform in the legal system. It analyses William Godwin’s and Percy Shelley’s influence on her critique of the Swiss penal system in the episode of Justine’s trial in Frenkenstein. The article explores Mary Shelley’s contacts with reformist Basil Montagu: largely ignored as a source for her view of the legal profession, he was an active opponent of the death penalty and a radical reformer. On the basis of Bruno Latour’s Actor-Network theory it is argued that Mary Shelley was at the centre of a circle of mediators, who inspired the treatment of the law in the novel Frankenstein.