When a mysterious electronic device capable of telepathic communication surfaces in the village of Saltey, Albert Campion must determine if the invention is genuine or a dangerous hoax. Campion is summoned to the isolated hamlet to investigate the origins of a transistor held by two local schoolboys, a discovery that has attracted the attention of ruthless individuals willing to commit murder to secure the technology. The narrative follows Campion as he navigates the insular, suspicious community of Saltey, where the legacy of smuggling and modern scientific intrigue collide. The investigation forces him to confront a web of local secrets while protecting the boys from external threats who view the device as a prize of immense value.

Readers frequently highlight the atmospheric shift in this late-career entry, noting how Allingham blends her traditional detective style with the anxieties of the mid-twentieth century. Discussion often centers on the unique premise of telepathic technology, which serves as a catalyst for exploring the darker impulses of the village inhabitants. Critics often point to the balance between Campion’s understated investigative methods and the escalating danger posed by the antagonists. Many fans appreciate the way the author maintains her signature wit while addressing more modern, high-stakes themes of industrial espionage and moral corruption. The book is widely regarded as a distinct departure from the earlier, more whimsical entries in the series, offering a more somber and grounded tone.