Boiling, Bubbling, Bulbous, Boils

On February 2, 1894 Doctor Macartney received a letter from Dr. Henry Cooper, who had previously been missing for half a year.
Inside he discovers that there may be more involved than simply a doctor gone missing and instead a plague that could destroy the world as we know it.

(𝘓𝘰𝘰𝘮𝘴𝘩𝘰𝘸𝘳𝘰𝘰𝘮.𝘤𝘰𝘮, 𝘊𝘰𝘷𝘦𝘳 𝘴𝘰𝘶𝘳𝘤𝘦)