A personal visit from Mycroft Holmes with a request from the Prime Minister embroils Holmes and Watson in the pursuit of a blackmailer. Threats against the British population have been made and carried out as a stark message that the blackmailer means business.Holmes and Watson travel to Truro in Cornwall where the blackmailer says he will strike next. The townspeople are already falling ill and Holmes must act quickly to save lives. Finding a common thread to the illness, Holmes is able to prevent further deaths and has a lead on the blackmailer.A visit to a business in London and an intriguing trap identifies the culprit but a rare error by Holmes may allow the blackmailer to escape and avoid the gallows.