"Monstrously good." - Louise Welsh. London, 1823. Mary Shelley's real-life friend Isabella Baxter Booth is 'disturbed in her reason' - seeing ghosts and dependent on narcotics to escape a hellish life with an increasingly violent, deranged husband. Fearful of her own murderous impulses towards him, Isabella flees for her childhood home in Scotland, where she meets an ambitious young doctor, Alexander Balfour. He will stop at nothing to establish a reputation as a genius in the emerging science of psychiatry and he believes that Isabella could be the key to his greatness. But as his own torments threaten to overwhelm Alexander, is he really the best judge of which way madness lies?